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Need educated model/feature advice for oscilloscope for doing high-quality audio

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Franki:

--- Quote from: alm on February 17, 2011, 11:33:22 pm ---
--- Quote from: Franki on February 17, 2011, 10:56:02 pm ---as long as it doesn't exercise poor signal quality

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Sample rate and attenuator are usually worse. Not sure how critical this is for your use.

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That's something I've heard in other places too, especially for the low/mid price range


--- Quote from: alm on February 17, 2011, 11:33:22 pm ---
--- Quote from: Franki on February 17, 2011, 10:56:02 pm ---and is usable under non-Windows OSes, like FreeBSD, Linux, L4...

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Forget this. If you're lucky, you may be able to figure out the protocol (either by asking or reverse engineering) and write your own.

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I can't forget about it, unless it would have all the required features on its own. I'm a little experienced in reverse engineering digital protocols, but I really don't have the nerves to do a full USB configuration reverse engineering. Really, doing this with USB really sucks.

Franki:

--- Quote from: EEVblog on February 18, 2011, 02:41:55 am ---Almost every general purpose bench scope on the market uses an 8bit converter. Sure some like the new Agilent have a 12bit averaging mode, but it ain't the same as havign a real 12 or 16 bit converter with a low noise floor.

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This is a bit of a sad situation, as my intuition tells me that there are more people that want more than 8 bits of dynamic range. Hopefully the Agilent's 12 bit averarging mode stands up to its name and is not fully covered by its input stage noise or the like.

Also, as you already have an Agilent, can you tell me if this is the case?
I'm also interested to know whether the averaging mode of the Agilent averages adjacent samples or samples of different cycles (sometimes called multisampling)?

Thanks in advance


--- Quote from: EEVblog on February 18, 2011, 02:41:55 am ---I presume you wanted to capture data and do decent THD analysis or something?

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exactly. thd, frequency response and noise analysis on inputs vs outputs, power supply, adjacent channels and on individual components at different test waves (first 100Hz, 1kHz, 10kHz broad and then finer on sine, square waves), then making frequency response analyzes (sweeps, white - pink noise) this is why I need differential calculations, rms/effective value calculation and a fft spectrum analyzer is real handy for that too.

Franki:

--- Quote from: NiHaoMike on February 18, 2011, 08:09:08 pm ---The best sound card does 192kHz sample rate at 24 bits with an analog bandwidth of about 20kHz. That would work fine for line level audio, but you won't be able to see the carrier transitions in a digital amplifier.

For a good analyzer software, try http://baudline.com/ .

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of course, but finding a laptop with such a high quality sound card isn't easy. Plus I really doubt they deliver the full 24 bit of accuracy, but even 16bit would be enough.

I have such a sound card in my PC, but in a laptop you basically need an onboard sound card(since most laptops don't have expansion card slots), and from my experience, many onboard sound chips really suck when it comes to being immune to noise from digital signals especially on the supply lines, even the more expensive ones. You have all kinds of whirring, and you can't just filter it out with a ferrite choke or metal shielding since it is on the supply line, and you can't just easily put an auxillary power supply(that is supposed to be mobile) just for the analog amps on your onboard sound card.

So, in conclusion, unless you have a good quality sound card specifically immune to noise, foremost HF noise, on the supply line or with an additional power supply connector, which are most likely found on dedicated ATX style PC expansion slot sound cards, your sound card is useless for doing audio oscilloscopy and actually useless for doing any serious audio recording.

It's not that the internals of digital scopes don't produce HF noise, but a) the manufacturer knows exactly what's in the scope, so he may exactly know what kind of noise there is and can account for required shielding, HF-suppression etc... where he wants and how he wants, whereas in a PC, no manufacturer can really know this, and most components aren't shielded inside of the PC casing and b) you probably don't have as big HF power variation as in a PC (hard drives, disc drives, current hungry cpus and graphic cards with maybe the exceptions of fans), and even if, the manufacturer can account for that and put adequate chokes, capacitors and other HF voltage stabilizing in the power line.

Franki:

--- Quote from: Hero999 on February 18, 2011, 09:29:26 pm ---I've never seen the point of a 192kHz sample rate for audio, it's just overkill, anything above is more than good enough and anything above 64kHz is probably imperceivable, even to someone with the best hearing.

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Yeah, the 192kHz audio sample rate, you really just need it for intermediate processing, especially non-linear computations/effects like speed changes, convolvers and other fancy stuff to not degrade quality

Franki:

--- Quote from: NiHaoMike on February 17, 2011, 11:22:29 pm ---You might also need to monitor the drive signals to high side MOSFETs, another place where an isolated probe is the only proper way to do it.

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This is what I'm mostly concerned of. I still have active probes from my old hameg 20MHz from the early 80 ies, but I have no clue whether they would be compatible to my new scope.

If not, how comes that there aren't any active probes for the Agilent 2000 series on their site http://www.home.agilent.com/agilent/product.jspx?nid=-536902770.0.00 just 1000, 3000, 5000 etc... series

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