Techmoan video: Shaving Compact Discs to improve the sound

[Ed.Kloonk]

Today I'm using a special lathe that cuts a 36º edge into a CD to improve the sound quality. Is this madness...I aim to find out.

[pcprogrammer]

Yes that is one for the audiophoolary to enjoy.

[golden_labels]

You are ignorant of physics. His Audacity experiment shows no difference only because computers represent waveforms as numbers. The program was operating on a squareish approximation of a true analog wave, rounding values to the nearest integers. Not to mention the recording device is using cheap ADC, that exaggerates that error. If you compared both outputs with a precise analog instrument, like your ears, you would clearly hear the difference. /S

[pcprogrammer]

There was no ADC, because he just used the optical fiber output, so all digital. A simpler test he could have done was to stick the CD's in a computer CD reader and get the .wav files directly from the CD and use a binary compare of the two files. No need to fiddle with Audacity.

No doubt in my mind they will be identical, physics or not. And like he said in the video, when a CD has read errors it can't recover it will cause hiccups not less bass or treble.

And yes, most likely you are pulling my leg

[TimFox]

Around 1990, besides the great Armor All^TM on CDs craze, there was also the Green Magic Marker on CD rim procedure.
From a fact-check site:  https://www.snopes.com/fact-check/bewaring-of-the-green/

[Haenk]

Not only is this (of course) nonsense, but it will in fact damage your CD over time. The metallic layer is sealed, removing the sealant might/will lead to disc rot.

And: If this would make a difference on your CP player, it certainly requires servicing - it's broken 

[ataradov]

Too much effort. My $900 magic stones placed around the room do the same thing.

To be fair, we don't really know what are the real profits in that industry. But then again, people buy JPEGs of monkeys for a lot more money.

[AVGresponding]

Around 1990, besides the great Armor All^TM on CDs craze, there was also the Green Magic Marker on CD rim procedure.
From a fact-check site:  https://www.snopes.com/fact-check/bewaring-of-the-green/

The marker pen bollocks was even touted around in respectable Hi-Fi publications, back in the day (no I never tried it).

[golden_labels]

You know, what makes me simultaneously dying from laugher and pitying some of people, who meticulously shaved their CDs and painted the edges? Physical albums in good condition are having financial value. Imagine there is a persone out there, who has a bunch of now rare CDs, which would be wort 5–10× the original price. If not that they shaved the discs.

Producer’s website also claims the technology improves data media. I will not ask if it increases resolution of my JPEGs. Instead I would ask how a disc, shaved with precision worse than offered by a medieval lathe, behaves at 52× speed. I will not try testing that in my drive.

[TimFox]

American coins (dimes and above) are still "milled" or "reeded" around the edges, a procedure dating back to when one could shave a bit of silver from each of many coins to amass silver metal at the expense of honest citizens.

[helio0centra@gmail.com]

With a digital format you either get it or you don't. There's no varying quality like analog. If your CD or laser is bad it skips.

[fourfathom]

With a digital format you either get it or you don't. There's no varying quality like analog. If your CD or laser is bad it skips.

Not exactly.  CDs use Reed-Solomon FEC, so most bit errors get fixed losslessly.  But if the errors are too much for the FEC then the next recourse is interpolation through the bad patch.  If the damage is too bad then you get a digital skip.  Interpolation is lossy and might possibly be noticeable to a "golden ear" (not mine).  So, if there were some way to reduce the need for interpolation then the audio quality might be improved.

Don't get me wrong:  green markers, beveled edges, weighted CD platters, and all that other crap do nothing but provide a way to spend more money on your system.  But CDs aren't all or nothing, there's a zone there.  Probably imperceptible, but it's there.

[pcprogrammer]

I wonder about that interpolation bit if that also applies for a CD reader in your computer when it reads "digital data" and not "audio data". I assume that it will only do this interpolation when it has read part of the audio data stream, detects that there are errors, tries to resolve the errors, can't and will then interpolate between previous and next samples.

Which means that it is software, and that it can depend on commands send to the drive, and when reading data as a binary file it will not use the interpolation scheme.

Furthermore a brand new CD will most likely be read almost error free and renders Techmoans tests somewhat invalid. The difficulty in doing a test that can be repeated in a valid manner, is that creating two exactly the same damaged CD's to invoke the same error correction is almost impossible. With a single CD that has errors it can only be done once, and it might improve back to the original behavior, but there is no way of proving that it is actually due to the shaving.

Interesting to think about though.

[fourfathom]

I wonder about that interpolation bit if that also applies for a CD reader in your computer when it reads "digital data" and not "audio data". I assume that it will only do this interpolation when it has read part of the audio data stream, detects that there are errors, tries to resolve the errors, can't and will then interpolate between previous and next samples.

Yes, that's how I understand it.  I should have said "audio CDs".  I honestly don't know what type of error correction data CDs use, but there is a spec for it (Yellow Book?)  I can't imagine that they would do interpolation on data.

[Jr460]

Hang on a second.

All digital, nothing changes, it is all the same.   Correct, but......

Music, making, it playing it, mixing it live for people, etc is a side line.

We have a little problem with jitter.   Now this came up because of AES/SPDIF digital formats.   They have no fixed sampling rates.  The sampleword/bit clock is recovered from the data stream.   Based on the data the sample clock can shift a bitt back and forth, jitter.   Some people say they an hear it all the time.   It is regarded as problem in pro audio that pro devices have an BNC jack to two to accept to to provide word clock to other devices.

Jitter in AES/SPDIF is very subtle.   it is a slight FM modulation of all the special components.   The same thins happens with tape to a turn table, but is listed as wow and fultter.

Jitter in digital audio systems is real, but the interface chips for along time have done things to reduce it, as talked abut already an external word clock, or using  a ddifern PLL to cleanup word clock from the bit recovery clocking.

No is where we get to the snake oil.   A Cd spins at it's rate can vary, thus the digital signal coming from the CD/DVD will have jitter.   That is true, however after all the error correction the bit clock used to recover the data is not the same or related to the clock that pumps out the samples.   For a CD that is defined as 44.1K.   If the CD speeds up, slows down, nothing changes the rate the samples are shipped to the D/A convertor.   This means no jitter from mechanical system.


Cut, trim, green maker all you want, either the optics pick up the pits and it turns into a sample, or it doesn't.

[ataradov]

If the CD speeds up, slows down, nothing changes the rate the samples are shipped to the D/A convertor.

And the samples are "shipped" based on some magical jitter-free clock source?

That 44.1 kHz generated from the local clock source, it is not informed by anything on the CD. So the quality of the clock going to SPDIF and DAC is the same.  SPDIF would incur some clock recovery jitter, of course, but it would not necessarily be worse than the source jitter. There is a good chance that receiver would be able to celan up the clock and would produce cleaner signal than DAC from the CD directly.

I'd also like to see credible sources showing that jitter matters in any way.

[pcprogrammer]

I guess the digital jitter will create some harmonics but with modern oversampling and digital filter techniques they will hardly be audible.

And don't forget it is all based on individual perception anyways. A recording made of some orchestra will almost always differ form the real thing. There are so many factors in the recording chain. You have the microphones, pre-amplifiers, mixing desk, equalizers, master recorder and most important the sound engineer. If the sound engineer is not so good, the recording will suck.

The fun part in it all is that the audiophiles often state that the warmth is in the imperfections. Take the debate about analog versus digital synthesizers. "The analog ones sound so much warmer" is the claim. And why, because of the imperfections. Drift between the oscillators, differences in the filter characteristics between the channels, etc. A good digital imitation takes this into account

[golden_labels]

American coins (dimes and above) are still "milled" or "reeded" around the edges, a procedure dating back to when one could shave a bit of silver from each of many coins to amass silver metal at the expense of honest citizens.

Only if the shaving was so extreme that it would put the recipient at risk of having the coin rejected by the next person/institution downstream.

Gold and silver are not very durable and coins made of them are losing material or get damaged in circulation due to normal wear. They are so prone to damage, that one method to shave coins was by shaking violently a bag with money and collecting dust produced when coins hit each other. So it was normal that most currency was missing some material and no one would care, except for the aforementioned extreme cases. It became even less relevant when coins started to be used for their nominal value and not actual precious metal content.

The violation was not against other people, but against the treasury. People engaging in shaving were doing something, that was perceived as stealing from the state, or acquiring wealth without paying taxes. And you know there is no greater crime on this planet than not paying taxes.

[Haenk]

I'd also like to see credible sources showing that jitter matters in any way.

Sorry, no link to quote, but I read a while back, that this is in fact a huge problem in production. Solution is to use a master clock and sync all digital inputs to it.

[SiliconWizard]

The whole idea if you want *objectively* better than audio CDs without resorting to voodoo (because 1. they are still only 16-bit, 2. as said above, yes they often have read errors depending on the state of the CD, how much dirt and scratching there is, how dirty the laser lens is as well, etc, in which case the CD player will correct errors to an extent and this may degrade audio quality obviously when then BER is greater than what can be fixed losslessly, and 3. yes you can have nasty jitter issues if the player is meh)...

just don't use CDs. Just play 24-bit audio using any basic computer (could be a RPi or whatever) through a decent DAC, and you'll be eons above anything a $100k+ voodoo CD setup can buy you for a couple hundreds bucks if that.

[fourfathom]

I'd also like to see credible sources showing that jitter matters in any way.

Sorry, no link to quote, but I read a while back, that this is in fact a huge problem in production. Solution is to use a master clock and sync all digital inputs to it.

This has always puzzled me.  I have a friend who is an occasional recording engineer, and he was always claiming that reading CD audio off a regular non-synched drive caused big problems.  (Of course he also used green marking pens back in the day).  As I see it, as long as the CD drive can read faster than the stream rate then the data is read in buffered chunks and no fancy clocking is required.  If the format is audio CD then the implied sampling rate is 44.1 KHz and that's all we need to know. Once processing is done, if you want to drive an ADC to get an audio signal then the only place jitter can be introduced is the ADC clock.

Now I can conceive of a system designed so badly that precision clocks are required at each interface, but is that actually the case?

[pcprogrammer]

The whole idea if you want *objectively* better than audio CDs without resorting to voodoo (because 1. they are still only 16-bit, 2. as said above, yes they often have read errors depending on the state of the CD, how much dirt and scratching there is, how dirty the laser lens is as well, etc, in which case the CD player will correct errors to an extent and this may degrade audio quality obviously when then BER is greater than what can be fixed losslessly, and 3. yes you can have nasty jitter issues if the player is meh)...

just don't use CDs. Just play 24-bit audio using any basic computer (could be a RPi or whatever) through a decent DAC, and you'll be eons above anything a $100k+ voodoo CD setup can buy you for a couple hundreds bucks if that.

As nice as that sounds, you still have to source your audio you want to listen to. And as long as that is 16bit 44.1KSa/s up scaling to 24bits won't make it better. But it seemed most of us did not care much about that quality because we turned to MP3 players and MP3 is a compression with loss of quality. Depends a bit on the selected rate but loss it gives.

Then came flac and ape, which are lossless algorithms but still based on 16bit 44.1KSa/s for as far as I'm aware.

So you would need "hi definition" audio with 24bit and maybe higher sample rates. However the last CD I bought was ages ago and I transferred all the ones I have to my hard disk and that is what I listen to when I want music. No idea what the latest state of technology is in respect to audio recordings.

I'm no audiophile and will never buy expensive amplifiers, special cables or hefty speakers, because I most likely won't hear the difference anyway. I play my music on my computer through a Cambridge Computer sound system, with one small bass speaker and 4 little satellite speakers, placed on the ground obscured by couches. And for me it is perfect as background sound.

[pcprogrammer]

I'd also like to see credible sources showing that jitter matters in any way.

Sorry, no link to quote, but I read a while back, that this is in fact a huge problem in production. Solution is to use a master clock and sync all digital inputs to it.

This has always puzzled me.  I have a friend who is an occasional recording engineer, and he was always claiming that reading CD audio off a regular non-synched drive caused big problems.  (Of course he also used green marking pens back in the day).  As I see it, as long as the CD drive can read faster than the stream rate then the data is read in buffered chunks and no fancy clocking is required.  If the format is audio CD then the implied sampling rate is 44.1 KHz and that's all we need to know. Once processing is done, if you want to drive an ADC to get an audio signal then the only place jitter can be introduced is the ADC clock.

Now I can conceive of a system designed so badly that precision clocks are required at each interface, but is that actually the case?

I think this has to do with digital mixing systems where the streams are all digital from different sources. Then it might need a master clock to make it work. With just a single digital source connected to a digital amplifier, I guess the data stream will just be buffered a bit (maybe 1ms or so) and send to the DAC at regular intervals based on the sample clock. As long as the data comes in at a steady pace a little bit of jitter does not matter.

[fourfathom]

Now I can conceive of a system designed so badly that precision clocks are required at each interface, but is that actually the case?

I think this has to do with digital mixing systems where the streams are all digital from different sources. Then it might need a master clock to make it work.

OK, I can see that.  If you use buffering for these non-master-clocked interfaces then you need to embed a timestamp or timing feedback, and I guess the format doesn't provide that.  And in a multi-source system with no master clock you will eventually get slips or overruns.  Reminds me of the telecom networks I used to design equipment for.  We did all sorts of mapping tricks to carry quasi-synchronous payloads through synchronous networks.

[pcprogrammer]

I think that nowadays it will all be done on a computer where all the data is present on the hard disks and tracks are shifted in time and cut in pieces and then mixed together into a final track.

There are loads of youtube videos of new music producers that use software like Ableton live, where they record the different tracks and then produce a final song. Like for instance Rachel K Collier. https://www.youtube.com/c/RachelKCollierRKC

[coppice]

Then came flac and ape, which are lossless algorithms but still based on 16bit 44.1KSa/s for as far as I'm aware.

I'm not sure about APE, but FLAC can be pretty much any bit depth or sample rate you like.

[fourfathom]

I think that nowadays it will all be done on a computer where all the data is present on the hard disks and tracks are shifted in time and cut in pieces and then mixed together into a final track.

That's how I was doing it 20 years ago.  Multi-take multitrack digital recording, time synch via click-tracks (not clock sync, this was for human use), some recorded live, some recorded in the studio, others sent in from remote locations (not real-time), etc.  I don't know what process requires all the clock synchronization, but perhaps there is one.

[SiliconWizard]

Then came flac and ape, which are lossless algorithms but still based on 16bit 44.1KSa/s for as far as I'm aware.

I'm not sure about APE, but FLAC can be pretty much any bit depth or sample rate you like.

Of course. I have a ton of 24-bit FLAC files. There's a number of retail sources where you can buy them from. (I'm not talking about pirating. Although you can probably find some stuff using that too.)

[pcprogrammer]

@SiliconWizard. Can you hear the difference between 24bit and 16 bit versions of the same music. I have never tried it, so no idea if I would.

[DavidKo]

I was quite surprised with his procedure. I will read both cd in computer and compare the data. I must say that his approach was very nice.

[rsjsouza]

Techmoan's videos are quite interesting, and this one didn't disappoint. Audiophoolery aside, this was revealing of the lengths people go to try and scam others.

[Zero999]

That video appeared in my recommendations. I smirked, thought what a load of bollocks and didn't bother watching it. I wonder if that happened to anyone else here?

[ataradov]

I think the tests here were not really necessary. They were just for content. There is absolutely no way to reproduce any differences and this is known in advance.

The video is just to show off a goofy device from the past.

[SiliconWizard]

@SiliconWizard. Can you hear the difference between 24bit and 16 bit versions of the same music. I have never tried it, so no idea if I would.

Yep. As long as the material is really 24-bit mastered content, and not just 16-bit content requantized. The former is now available from various resellers.
The main point is that due to the extended dynamic range, audio that was properly mastered @24-bit instead of 16-bit uses much less heavy compression. Excessive compression for 16-bit CD mastering is very common. And that's definitely annoying. Now whether you'll hear the difference really depends on the kind of music that is. For some kinds, it doesn't really matter if there is "heavy" compression or not. For others, it definitely does.

[TimFox]

I recently attended a live concert that featured Olivier Messiaen's "Quartet for the End of Time", which has an extremely large dynamic range (far greater than young peoples' boomedy-boom) between the loudest and quietest sections.
During the lowest loudness sections, the hall's ventilation was clearly audible.  Nevertheless, the details of the acoustic instruments were clearly audible to the unaided ear.
I didn't have my portable sound level meter with me, and it was probably out of range anyway.
With non-sinusoidal musical waveforms, what is the quantitative relationship between the required bit depth and the overall dynamic range?

[DavidKo]

I think the tests here were not really necessary. They were just for content. There is absolutely no way to reproduce any differences and this is known in advance.

The video is just to show off a goofy device from the past.

You are looking on it with wrong optics. You must look at it as you do not know anything about it and want to buy this CD destroyer second hand. Everything written about device itself can be true, except that it is nonsense from the CD point of view. From the optical point of view the black maker on the side will work the same way independently on the angle, even without cutting it. Marker will simply absorb the light in the same amount with very small influence of the angle. On the other hand the wave guide effect itself cannot work, first there is no total reflection on the aluminized part and additionally the light is scattered with the data, so there will be almost no light on the edge, except reading really close to the edge.

By the way most of the Techmoan's videos show devices from the past and this is nice video about scamming people, which happens all the time. I expect that in few year someone will recreate this device and will sell it in the same way (probably including 5 star reviews in magazines).

[AndyBeez]

I agree grinding the edge improves balance, but do compact discs read from the inside outwards? I don't know as I'm no connoisseur de audio.

Anyway guys I need to know this; will angle grinding improve the video signal (SN ratio) from a PWM encoded 1980s LaserDisc? The LaserDisc is a quasi analog system therefore, angling the edge should give near 4K performance from a VHS quality disc. Surley this is just exponential extrapolation ?

[golden_labels]

As for the light absorption, thre is no particular requirement regarding the marker and dye it uses.

Keep in mind CD readers use 780nm light, which is near infrared. Dyes are designed to cover visible spectrum and neither anyone cares if they absorb IR nor you can test that with your naked eye. While one can argue that some pens use blue dye to obtain black color, and that it absorbs red and likely NIR, that can’t be said about pens using red dyes.

So that part can also be considered untrue, even if covering the edge in some paint would provide any benefits.

[NiHaoMike]

Anyway guys I need to know this; will angle grinding improve the video signal (SN ratio) from a PWM encoded 1980s LaserDisc? The LaserDisc is a quasi analog system therefore, angling the edge should give near 4K performance from a VHS quality disc. Surley this is just exponential extrapolation ?

No need to modify the disc, digitize it and run it through Nvidia DLSS. There are a number of examples of just how good upscaling can be nowadays.

[AndyBeez]

No need to modify the disc, digitize it and run it through Nvidia DLSS. There are a number of examples of just how good upscaling can be nowadays.

I also realised old LaserDiscs are too large to fit on this disc shaver  My theory about shaving is, if it really did work, it was because the first generation of CD players did not have the best lasers?

I recently upscaled some old family VHS-C content digitised to MP4. Took about a week of processing time, but the grain from the original camera's CCD is now really noticable sharp. GIGO.

[james_s]

Yes, CDs play from the inside outwards, and no, there was nothing wrong with the lasers in early CD players, the first players worked very well, later ones were mostly just less expensive to build.

[NiHaoMike]

I recently upscaled some old family VHS-C content digitised to MP4. Took about a week of processing time, but the grain from the original camera's CCD is now really noticable sharp. GIGO.

At least in theory, deep learning (that's what DLSS is - Deep Learning Super Scaling) can recognize what's noise and what's detail.

[onsenwombat]

I agree grinding the edge improves balance, but do compact discs read from the inside outwards? I don't know as I'm no connoisseur de audio.

Anyway guys I need to know this; will angle grinding improve the video signal (SN ratio) from a PWM encoded 1980s LaserDisc? The LaserDisc is a quasi analog system therefore, angling the edge should give near 4K performance from a VHS quality disc. Surley this is just exponential extrapolation ?

Remember to switch your laserdisc player power cables to >99.9% silver ones, otherwise your k's roll over and the system might be damaged.

On-topic, what a comedy gold. Been a while since I've had my dose of high-end audiophile lunacy, and this certainly made me chuckle few times.

[coppice]

@SiliconWizard. Can you hear the difference between 24bit and 16 bit versions of the same music. I have never tried it, so no idea if I would.

24 bit is extremely useful in a recording and production environment, as it means you can still get a good 16 bits after adjusting gains, applying various forms of processing, like compression, and so on. However, it is not necessary for distribution. If you can hear the difference between 16 and 24 bits from a distributed recording the 16 bit one must have been poorly prepared. Either the gains were messed up, or they didn't apply dithering properly.

Most recordings, even classical ones, are now much more compressed than in the past. This can be a good or a bad thing. In most situations capturing the full dynamics of an orchestral concert experience in the home means you have to turn up the quiet passages, and turn down the loud ones to avoid disturbing other people. However, even if you apply no compression at all, 16 bits properly dithered will capture all the dynamics your ears can detect.

[coppice]

I recently upscaled some old family VHS-C content digitised to MP4. Took about a week of processing time, but the grain from the original camera's CCD is now really noticable sharp. GIGO.

At least in theory, deep learning (that's what DLSS is - Deep Learning Super Scaling) can recognize what's noise and what's detail.

DLSS is basically "making shit up when there is no genuine information to work with". Just as an artist can take a messy picture and air brush it into something nice looking, so can DLSS. That's good for making things look more pleasant, but there is no actual detail in there. Don't expect anything in the details to be genuine. It can often look "clear" when its totally bogus.

[NiHaoMike]

24 bit is extremely useful in a recording and production environment, as it means you can still get a good 16 bits after adjusting gains, applying various forms of processing, like compression, and so on. However, it is not necessary for distribution. If you can hear the difference between 16 and 24 bits from a distributed recording the 16 bit one must have been poorly prepared. Either the gains were messed up, or they didn't apply dithering properly.

Most recordings, even classical ones, are now much more compressed than in the past. This can be a good or a bad thing. In most situations capturing the full dynamics of an orchestral concert experience in the home means you have to turn up the quiet passages, and turn down the loud ones to avoid disturbing other people. However, even if you apply no compression at all, 16 bits properly dithered will capture all the dynamics your ears can detect.

It's also useful for playback if you want to do something other than just play the file bit perfect. For example, if you apply equalization, some frequencies will have to lose resolution. With 24 bit playback, you'll have a lot of room to keep the usable resolution to 16 bits or more.

[BrianHG]

If you can hear the difference between 16 and 24 bits from a distributed recording the 16 bit one must have been poorly prepared. Either the gains were messed up, or they didn't apply dithering properly.

And that's the kicker.
16bit done right is superb under 99.99% of the use cases.  (Unless you are trying to encode the full authentic dynamic range of gunfire and explosions, however, who has a sound system which can effectively destroy your internal organs...)
I can only, if I tried, make a case for a higher sample rate than 44.1Khz, and it doesn't need to be much higher.

[Fixpoint]

I wonder about that interpolation bit if that also applies for a CD reader in your computer when it reads "digital data" and not "audio data". I assume that it will only do this interpolation when it has read part of the audio data stream, detects that there are errors, tries to resolve the errors, can't and will then interpolate between previous and next samples.

This doesn't make any sense from any viewpoint. It is important to understand what interpolation actually is. In order to make my point simpler, let us assume a very simple form of interpolation by taking the average.

• The "average" is a statistical measure, namely the arithmetic mean, defined to be the sum of data points, divided by the size of the set. However, a non-audio CD doesn't contain any data points, so the average is not defined. It just doesn't make sense to talk about the "average" when working with a non-audio CD because you are talking about things that don't exist/are not defined.
• Maybe you think because any data can be encoded as numbers, this gives us a meaningful definition of an average. That is not correct. The average would only be defined on the encodings but not on the represented data itself. Illustration: When we have a bit sequence representing an "A" and another sequence representing a "B", what does the average of their numerical encodings mean in the data domain? Nothing.

These points extend to all other forms of interpolation.

[pcprogrammer]

First of all there is no mention of average, but interpolation between possibly multiple samples to reconstruct what it originally might have been. There are all sorts of algorithms to do such an interpolation. Does not have to be linear.

Furthermore it was about reading the audio tracks on a computer. The question was about if the computer makes a distinction when reading it as digital data. In other words if a different method is used when playing the CD in your computer or reading it as digital data. In both cases it concerns the audio data, and not some binary text or program.

Edit: you reworded your post, while I was writing my reply

[Fixpoint]

Edit: you reworded your post, while I was writing my reply

Yes, I noticed that I had written my response with the simplest example in mind which could invite people to say "it doesn't apply to the general case". Oh dear. Well ... it does!

There are all sorts of algorithms to do such an interpolation. Does not have to be linear.

Well, what I tried to explain is that this exact statement has nothing to do with the problem at hand, that's the whole point. Linear or not, when talking about interpolation we are talking about statistical methods. For those to apply, you need to data points which we don't have on a non-audio CD.

Furthermore it was about reading the audio tracks on a computer. The question was about if the computer makes a distinction when reading it as digital data.

When the audio CD data is treated as non-audio, you already have given the answer yourself. In this case, the hardware cannot apply any kind of interpolation since there are no data points to interpolate. If non-audio data cannot be read, this is called an I/O error. Hardware that says "oh my, I can't read those bits! but never mind, I'll just make some up real quick" would be useless.

However, AFAIK the hardware can be configured to ignore read errors and continue reading.

[pcprogrammer]

Let me rephrase it then. Are there markers or some metadata on an audio CD, based on which the computer can tell it is reading audio data and treat it differently then digital data.

The point was about not needing audacity to do the comparison between the two CD's, and just read the data from the CD with the computer. And there I wondered if the computer could do the same error correction as a CD player uses.

[Fixpoint]

Are there markers or some metadata on an audio CD, based on which the computer can tell it is reading audio data and treat it differently then digital data.

Yes. Audio CDs adhere to the Red Book standard.

And there I wondered if the computer could do the same error correction as a CD player uses.

Yes, it can & does. If you insert an audio CD into your drive, the hardware will detect that it is an audio CD. The driver software will then suggest to you to play it as an audio CD. However, you can write software that tells the driver "no, please read the CD as non-audio data" which will put the hardware in a different readout mode (fast than 1x speed, different kind of error correction etc).

[wraper]

Let me rephrase it then. Are there markers or some metadata on an audio CD, based on which the computer can tell it is reading audio data and treat it differently then digital data.

The point was about not needing audacity to do the comparison between the two CD's, and just read the data from the CD with the computer. And there I wondered if the computer could do the same error correction as a CD player uses.

Audio CD and data CD are entirely different formats. Audio CD has no file system. The problem with audio CD format is that a compromise of data integrity was made which allows a bit more usable data to be stored (data CD can store less data), but error correction used is quite weak and does not provide guarantee there was no error during reading. Good audio ripping programs like Exact Audio Copy read audio CD multiple times at slow speed to ensure good data integrity.
Actually compromise is understandable. Early CD audio players had no data buffer (it would cost insane money in early 80's) and read at 1x speed, therefore even if reading error could be detected for sure, player would not be able to try reading it again without interrupting the sound.

[Ed.Kloonk]

Gee, I'm dusting off my memory banks here. From what I remember...

The ATAPI interface got sent back different sized packets depending on whether or not it was an audio CD.

The first gen cdrom readers were terrible at aligning the blocks to the exact position requested by the driver. The error correction for byte misalignment with filesystem blocks was done by the driver, I believe. Later the raw CDDA blocks had to be manually aligned with specific software. Better drives (2nd gen) such as Plextor which I owned a few of, fixed this CDDA read-back alignment issue.

Yet, the error correction of actual corrupted data read off the CD surface whatever the format was accomplished by the drive's own firmware. Early ones were hit and miss in how well they dealt with read-back problems. You got what you paid for.

[golden_labels]

error correction used is quite weak and does not provide guarantee there was no error during reading

As a minor correction: data CDs have no such guarantee either. The difference is quantitative, not qualitative.

Mode 1 sectors⁽¹⁾ of “data” CDs (CD-ROM, yellow book) offer higher resilience against data corruption than “audio” CDs (CD-DA, red book). But they are not immune to read errors in yes-no sense; not even in “almost surely” sense. Merely “less likely”, which is also diminished by much higher read speeds.

The amount of data, that contributes to read errors being detected on data CDs, is also minuscule: less than 0.2% of the capacity. The rest is used for data encoding, but only that 0.2% is used to detect errors.

While standard audio CDs are indeed having a bit more capacity than data CDs, the massive advantage you may see in some releases is achieved in a different manner. Since audio CDs are read at much lower speeds and read errors are not a critical issue, they can push track separation to its limits, beyond what is permitted by the standard, and pack more tracks into unit space.

⁽¹⁾ But not Mode 2 sectors. Those are still taking slightly more space, but without added protection.

[jonovid]

seen the video-
in my opinion the platter drive machine can be modified for disc polishing out heavy scratchs on the play surface , here is were the
noticeable difference between data and no data is realized.  not rim trimming!
as most disc repair machines are not as robust as needed to hold the disc when applying pressure when polishing.

[Jeff eelcr]

CD's are not all manufactured perfectly I have seen quite a few that had to have the
edges shaved in order to work correctly (extra plastic on edges) can cause rubbing
and jaming problems in changers if not the correct size.
Jeff

[Nominal Animal]

what is the quantitative relationship between the required bit depth and the overall dynamic range?

They're basically the same thing, about 130 dB ≃ 21 bits.

Human hearing is based on small tuned antennae (stereocilia connected to cochlear hair cells) which have roughly logarithmic response.  Each cell is activated by a specific frequency, and there are around 15,000 of them in each ear.  The amplitude range at which these respond to sound varies based on the frequency, but in the middle frequencies (with most cells), the dynamic range is 120-130 decibels, corresponding to 20-21 bits.

The detail where required bit depth and dynamic range differ, is when we combine a loud sound with a quiet sound: especially low frequency loud sounds override quieter higher frequency sounds.  This is why dynamic compression "works": by having the signal "clip", the effect is similar to how in the ear, loud low frequency signals "hide/silence" higher frequency signals.

[Zero999]

The dynamic range of the human hearing might be 120 to 130dB, but it's not safe to be exposed to sound at the higher end of this range. The dynamic range of a CD at 96dB is more than sufficient to cover the dynamic range of sound which is safe to be exposed to.

[Nominal Animal]

Human perception of sound is wildly strange, though.  Now that you know that the human hearing organ is basically a spectrogram with 13,000 or so bins and 100+ dB of dynamic range, think about how it is possible for a person (with hearing only in a single ear) to be able to listen to two different people at a time?  Or even detect the voice of someone familiar in a babbling crowd?  I'm tempted to say the human brain is a pattern detector, but its is so much more than that, because in detecting a voice (be it human, animal, event, musical instrument, or whatever), the time component is also involved; and it can detect a huge amount of different sounds at a time, even in parallel –– like running water, birdsong, leaves rustling, and two people talking at the same time.

It is even possible to generate sound that is perceived as quieter than silence.  This sound is just shaped noise modeling the sensitivity of sound perception, i.e. the human psychoacoustic model.  To the brain, it contains nothing interesting, and just shifts the "base" threshold of detection, so that even sounds generated by our own bodies (heartbeat, blood flow in veins) get attenuated: everything becomes "more quiet".

In audio compression, the psychoacoustic model has been used ever since MP3 came to be, to distribute the quantization noise, yielding better perception of the sound.  (Essentially, it is about controlling what information is conveyed, and where in the spectrum the errors/noise due to compression and quantization is placed in.)

Because of the brain, I bet that things like lighting (as in whether you are in a dimly-lit room with soft yellow-orange lights, or harsh cold blue-white light) and especially scents have more effect on the experience than things like exactly which amplifier or amplifier settings you use.

[AVGresponding]

 





 

[PlainName]

They still have a metallic layer, don't they? Ergo magnets must affect them, and anything that does that affects the nois sound.

I think they've missed a trick, though. They should supply 'magnets' with a sticky surface so you can see they're effective when they lift a CD.

[Nominal Animal]

If I didn't have scruples, I'd start selling audio-enhancing candles for the audiophɪ̥̊les.  The sales pitch would extol the enhanced air carrier mechanisms for the audio waves, producing a richer listening experience.

[PlainName]

Ding!

Apparently A UK museum are experimenting with smells to enhance the experience. So you could sell 'smellopacks' for DVD films, so that when some particular scene is playing, the viewer can smell what's on the screen.

Of course, it's only once they've bought the pack that they find out it's a box of candles and they have to manually light and extinguish the appropriate one at the right times. But they'll get a timesheet to help them.

[golden_labels]

You are late with that idea: 4D cinema. Horrible experience!

[PlainName]

But they cost a fortune set up. A box of scented tealight candles are far cheaper (but should still sell at a premium price).

[AndyBeez]

Degaussing CDs... 100% Dodgy Technology. If CDs were Magneto Optical Drives (MODs), then maybe this might boost 'rewrite integrity'.  One test could be holding an AM radio near to the box and listening to the EM field. Or use one of @Eevblog Dave's home made EM probes. If it actually produces any EM field 

+ or just place a compass needle on the box and see if it spins. Bets are, nothing happens.

@Techmoan, I would love to see the shkematic for the PCB. Looks like someone put a lot of thought into this box with it's fading green LED

[coppice]

You are late with that idea: 4D cinema. Horrible experience!

The ones I've experienced in Disneyland were good fun. Not something you'd want regularly, but a fun occasional experience.

[Ben321]

I wonder about that interpolation bit if that also applies for a CD reader in your computer when it reads "digital data" and not "audio data". I assume that it will only do this interpolation when it has read part of the audio data stream, detects that there are errors, tries to resolve the errors, can't and will then interpolate between previous and next samples.

Yes, that's how I understand it.  I should have said "audio CDs".  I honestly don't know what type of error correction data CDs use, but there is a spec for it (Yellow Book?)  I can't imagine that they would do interpolation on data.

Data CDs use an extra layer of FEC (in addition to the standard RS FEC) that uses a technique other than RS (I think it's convolutional coding or something). This is done per sector of data. Plus I think it also stores a checksum or CRC after each sector so it can tell if the data is correct after all FEC corrections have been performed when reading the disk. In fact, because of these additional FEC bytes and check bytes, there's actually less space available on a data CD than an audio CD.

[Ed.Kloonk]

From the wiki:
https://en.wikipedia.org/wiki/CD-ROM

Both Mode 1 and 2 sectors use the first 16 bytes for header information, but differ in the remaining 2,336 bytes due to the use of error correction bytes. Unlike an audio CD, a CD-ROM cannot rely on error concealment by interpolation; a higher reliability of the retrieved data is required. To achieve improved error correction and detection, Mode 1, used mostly for digital data, adds a 32-bit cyclic redundancy check (CRC) code for error detection, and a third layer of Reed–Solomon error correction[n 1] using a Reed-Solomon Product-like Code (RSPC). Mode 1 therefore contains 288 bytes per sector for error detection and correction, leaving 2,048 bytes per sector available for data. Mode 2, which is more appropriate for image or video data (where perfect reliability may be a little bit less important), contains no additional error detection or correction bytes, having therefore 2,336 available data bytes per sector. Note that both modes, like audio CDs, still benefit from the lower layers of error correction at the frame level

When a disc image of a CD-ROM is created, this can be done in either "raw" mode (extracting 2,352 bytes per sector, independent of the internal structure), or obtaining only the sector's useful data (2,048/2,336/2,352/2,324 bytes depending on the CD-ROM mode). The file size of a disc image created in raw mode is always a multiple of 2,352 bytes (the size of a block).[20] Disc image formats that store raw CD-ROM sectors include CCD/IMG, CUE/BIN, and MDS/MDF. The size of a disc image created from the data in the sectors will depend on the type of sectors it is using. For example, if a CD-ROM mode 1 image is created by extracting only each sector's data, its size will be a multiple of 2,048; this is usually the case for ISO disc images.

On a 74-minute CD-R, it is possible to fit larger disc images using raw mode, up to 333,000 × 2,352 = 783,216,000 bytes (~747 MB). This is the upper limit for raw images created on a 74 min or ≈650 MB Red Book CD. The 14.8% increase is due to the discarding of error correction data.

Code: [Select]

Format ← 2,352 byte sector structure →
CD digital audio: 2,352 (Digital audio)
CD-ROM Mode 1: 12 (Sync pattern) 3 (Address) 1 (Mode, 0x01) 2,048 (Data) 4 (Error detection) 8 (Reserved, zero) 276 (Error correction)
CD-ROM Mode 2: 12 (Sync pattern) 3 (Address) 1 (Mode, 0x02) 2,336 (Data)