Author Topic: Please recommend a scope (or other device) purely for audio testing.  (Read 13498 times)

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Offline uktonyTopic starter

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Hello all, new member here - apologies if this has been asked before. I did search.

I apologise for the length of this post - I tried to convey as much info as possible.

My primary interest is audio equipment (strictly hobbyist).

I do however like to measure what I build, and have some PC software and a FocusRite Scarlett 2i2 V2 for this purpose.

However, the frequency response is limited to around 80 to 90k at best with this setup, and I would like to measure beyond this.

Ideally I would like to measure to 500kHz or so.

Initially I purchased a Picoscope 2204A and used FRA4Picoscope https://bitbucket.org/hexamer/fra4picoscope/wiki/Home to perform frequency response and phase plots (but using a DLL provided with Excel).

Unfortunately the AWG in the Picoscope 2204A is limited to 100kHz, so this proved to be a limitation for me.

I also currently have an Owon SDS5032, however it's a struggle to get bode plot data out of that scope, despite having USB and a supplied application (I have tried several of the opensource offerings, however most of those are written for the SDS7102 and don't seem to return the correct data from my scope).

I then bought a Velleman PCSU200 which is not bad however the software is appalling, and it lacks any alternative so that's going.

I have since researched many options, and am struggling to come up with something suitable.

I have a very limited budget, and have looked at several of the device mentioned on this very blog including the Hantek / Sainsmart / Owon VDS102x / Intrustar etc. all of which seem to have there limitations - but as I'm only looking to perform basic audio measurements I don't believe sampling buffers / speed etc. are crucial to my requirement?

I've seen the Digilent Analogue explorer Discovery which looks to be a good device, however I feel it might be using a sledgehammer to crack a  nut for my requirement.

Additionally I have also looked at buying a Picscope 2206B (AWG extends to 1Mhz) however this is also costly...

So what would I like:
  • FFT / bode plotting
  • Downloadable data
  • Linux compatibility would be nice (to enable scripted testing)
  • An onboard DDS generator
  • USB connectivity *or* a method to store data (if not a USB scope)

I would appreciate any suggestions.

Thanks in advance,
Tony.

EDIT: I should have said - budget is £300 absolute maximum, and I would like to spend a lot less if possible!

EDIT(2): I'm just exploring options that I may have missed - for example I also found the 'Tsunami' (Arduino based audio analyzer) https://www.crowdsupply.com/arachnid-labs/tsunami - but I feel it's expensive for what it is. (£88 in the UK - and the only stock I could find).


« Last Edit: June 12, 2017, 03:37:22 pm by uktony »
 
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Online nctnico

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #1 on: June 12, 2017, 03:11:55 pm »
Digilent Analog discovery?
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline simone.pignatti

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #2 on: June 12, 2017, 03:19:08 pm »
the Pico 4262 is a good solution for audio testing, see the specs act pico website here
https://www.picotech.com/oscilloscope/4262/picoscope-4262-specifications
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Offline schmitt trigger

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #3 on: June 12, 2017, 03:24:54 pm »
You may still be able to find an used Audio Precision analyzer at a reasonable price.

AP has always been the gold standard of audio testing.
 

Offline uktonyTopic starter

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #4 on: June 12, 2017, 03:32:46 pm »
Digilent Analog discovery?

This is already on my list.

the Pico 4262 is a good solution for audio testing, see the specs act pico website here
https://www.picotech.com/oscilloscope/4262/picoscope-4262-specifications

Nice, but way over my budget. My budget is max £300.

You may still be able to find an used Audio Precision analyzer at a reasonable price.

AP has always been the gold standard of audio testing.

Again - way over my budget. I've seen these advertised for well over $2k on Ebay!!

 

Offline ruairi

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #5 on: June 12, 2017, 04:00:43 pm »
Tony,

Audio guy here, what do you need to test above 100k?  Or rather why?

Cheers,
Ruairi
 

Online nctnico

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #6 on: June 12, 2017, 04:08:12 pm »
Again - way over my budget. I've seen these advertised for well over $2k on Ebay!!
With some patience a good deal can be found. Also asking prices on Ebay are usually way too high.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline uktonyTopic starter

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #7 on: June 12, 2017, 04:30:39 pm »
Tony,

Audio guy here, what do you need to test above 100k?  Or rather why?

Cheers,
Ruairi

I have been experimenting with wideband preamps, along with HF distortion caused by bandwidth limiting.

And no, I can't hear any difference before anybody asks!!

This is purely experimentation.

 

Offline DaJMasta

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #8 on: June 12, 2017, 04:35:09 pm »
+1 to why so much frequency response.  I can hear to about 17.5kHz, so why would I care about tones that are hundreds of kHz?


Anyways, a good quality sound card and a software suite will get you the most detail for your money, but if they're designed as sound devices, they often don't support really high frequencies (you need 1Msample/s+ if you actually want to see stuff at 500kHz).

If you really need that frequency response for some reason.... you're going to have a tough time in your budget.  Any old scope can give you the bandwidth, but you're likely to get 8-12bits resolution (very low dynamic range for audio).  You can go with a high res scope like the 16 bit picoscope, but it's still not going to compete with the dynamic range and noise floor of a good quality sound card ADC.  They make specialized ADC modules and dynamic signal analyzers that are designed for acoustic and vibration measurement that can measure a couple hundred kHz with a high dynamic range, but then you're way out of your budget and don't get a generator.




So do you really need that kind of frequency response?  No professional audio analyzer can see tones or generate above a maybe 100kHz, and no person is going to hear into that range.... but if you're still convinced you need it, then you need to be looking for some real specialized equipment with a deep discount if your current scope isn't enough.
 

Offline ruairi

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #9 on: June 12, 2017, 05:20:46 pm »
Tony,

Audio guy here, what do you need to test above 100k?  Or rather why?

Cheers,
Ruairi

I have been experimenting with wideband preamps, along with HF distortion caused by bandwidth limiting.

And no, I can't hear any difference before anybody asks!!

This is purely experimentation.

I'm all for experimentation and verifying things myself but some very smart people have looked at this in the past.  We don't want huge bandwidths in an audio system, amplifying unwanted RF is not our goal.   With that in mind we are typically filtering on the input and low passing. 

I can't think of a mechanism for distortion introduced by input bandwidth limiting, input RF filters are typically passive and low order.  I guess that if they are st too low you could see small amounts of phase shift or rolled off response at the top end but neither should be present in a decent design.

If you have oscillation or other anomalies a scope will help track them down, and you should see higher distortion in the audible band.

The new Keysight 1000 series scope does have Bode plots in a wide range, not sure exactly where they stop.


 

Offline Fungus

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #10 on: June 12, 2017, 05:47:17 pm »
I have been experimenting with wideband preamps, along with HF distortion caused by bandwidth limiting.

Why would bandwidth limiting cause HF distortion?

Signal theory says the exact opposite - that bandwidth limiting is good!

Having said that: I'll second the Analog Discovery. It has the right combination of ADC bits, bandwidth, function generator and software for this sort of work.
« Last Edit: June 12, 2017, 05:51:08 pm by Fungus »
 

Offline uktonyTopic starter

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #11 on: June 12, 2017, 06:08:54 pm »
Well I found what must be old stock of the Tsunami - https://www.crowdsupply.com/arachnid-labs/tsunami

Which I'm hoping will do exactly what I want - https://github.com/arachnidlabs/tsunami-arduino/wiki/Measuring-Frequency-Response

It was £88 which was a bit pricey for what it is (was $60 at launch) but I'll report back if it's any good, although they don't seem to be available any more.

It doesn't have to offer 100% precision for my purpose anyway.

And most important of all it was comfortably inside my budget and leaves me with some pocket change to buy other goodies.

Thanks to all those who contributed - as I said in my opening post, I just wanted to be sure I hadn't missed any options.

Oh, and I take on board the comments about wide bandwidth - I just like to see exactly what my circuits are doing, regardless of total bandwidth - and this tool will just be a supplement to measurements made with PC software and Focusrite.


 

Offline DaJMasta

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #12 on: June 12, 2017, 06:58:29 pm »
I think part of the bandwidth point is that while it's interesting to see how they will perform at extended ranges, they will perform worse because of extending their range.  Widening the bandwidth of an audio circuit beyond the range you can hear artificially raises the noise floor, even in the audible range, even though you can pass through those components above the hearing threshold.  So to get the best noise performance, you generally want the smallest bandwidth you can afford.

At some level it's counter-intuitive, but it's how bandwidth works - the more you can narrow it down, the lower your noise will be in the area you are looking given the same inherent hardware noise.
 

Offline egonotto

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #13 on: June 12, 2017, 07:23:40 pm »
Hello,

uktony wrote:
"
So what would I like:

    FFT / bode plotting
    Downloadable data
    Linux compatibility would be nice (to enable scripted testing)
    An onboard DDS generator
    USB connectivity *or* a method to store data (if not a USB scope)
"
When I understand correct the tsunami is essential a DDS-generator.
The input has only 15KS/s.

I think the Analog Discovery is best to fit your demand.

Best regards
egonotto
 

Offline f5r5e5d

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #14 on: June 12, 2017, 07:32:03 pm »
for amplifier circuits for audio, whether op amp or discrete, stability verification requires 10s of MHz viewing BW at the least
 

Online David Hess

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #15 on: June 12, 2017, 08:15:34 pm »
I have never used them but Syscomp Design makes some instruments which may suit your needs.

http://www.syscompdesign.com/Instruments_ep_42.html
 

Online nctnico

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #16 on: June 12, 2017, 10:56:47 pm »
Another option would be to look for a network analyser. Say something which goes from several Hz to several MHz. These aren't cheap (although good deals can be found) but do save a lot of trouble. A network analyser is also useful for various other tasks like an LCR meter. I just wanted to mention this for completeness if it hasn't been mentioned already.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Someone

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #17 on: June 12, 2017, 11:17:50 pm »
Hello,

uktony wrote:
So what would I like:
  • FFT / bode plotting
  • Downloadable data
  • Linux compatibility would be nice (to enable scripted testing)
  • An onboard DDS generator
  • USB connectivity *or* a method to store data (if not a USB scope)
When I understand correct the tsunami is essential a DDS-generator.
The input has only 15KS/s.
The tsunami board has an input with phase/frequency measurement and a peak detector to estimate amplitude. So its a very basic network analyser with a broadband peak detector that will overestimate amplitude, limit the dynamic range, and hide non-linear effects.
 

Offline ruairi

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #18 on: June 13, 2017, 01:06:03 am »
Another option would be to look for a network analyser. Say something which goes from several Hz to several MHz. These aren't cheap (although good deals can be found) but do save a lot of trouble. A network analyser is also useful for various other tasks like an LCR meter. I just wanted to mention this for completeness if it hasn't been mentioned already.

The 50 ohm inputs / low max input levels on most network analyzers complicate matters, very few pieces on audio gear will be happy with those conditions.
 

Offline Keicar

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #19 on: June 13, 2017, 01:55:37 am »
for amplifier circuits for audio, whether op amp or discrete, stability verification requires 10s of MHz viewing BW at the least

Absolutely - no need for fancy analysis features at such bandwidth, but you do need a way to see oscillation and ringing at such frequencies - an audio amplifier that's behaving like an RF oscillator will draw excessive current and sound nasty, but detailed analysis at audio frequencies won't reveal the cause of the problem.
 

Online David Hess

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #20 on: June 13, 2017, 02:41:40 am »
for amplifier circuits for audio, whether op amp or discrete, stability verification requires 10s of MHz viewing BW at the least

Absolutely - no need for fancy analysis features at such bandwidth, but you do need a way to see oscillation and ringing at such frequencies - an audio amplifier that's behaving like an RF oscillator will draw excessive current and sound nasty, but detailed analysis at audio frequencies won't reveal the cause of the problem.

That is a different problem for which a standard oscilloscope will be more suitable than a specialized low frequency network analyser.  There is no reason the same instrument needs to perform both functions although I think it is a tragedy that DSOs which include waveform generators do not support multiple forms of low frequency high performance network analysis.

The CGR-201 that I linked seems to meet all of the requirements and operates up to 5 MHz as an oscilloscope and 10 MHz as a network analyser.
 

Offline mtdoc

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #21 on: June 13, 2017, 03:25:12 am »
The Digient Analog Discovery is likely perfect.

12 bit scope with 30MHz bandwidth (using BNC adapter)
10MHz AWG
Network Analyzer
Software with Linux SDK available (I think)

And check out this thread on Jaxbird's excellent audio analysis sotware developed for it.
 

Online nctnico

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #22 on: June 13, 2017, 06:37:20 am »
Another option would be to look for a network analyser. Say something which goes from several Hz to several MHz. These aren't cheap (although good deals can be found) but do save a lot of trouble. A network analyser is also useful for various other tasks like an LCR meter. I just wanted to mention this for completeness if it hasn't been mentioned already.
The 50 ohm inputs / low max input levels on most network analyzers complicate matters, very few pieces on audio gear will be happy with those conditions.
The Anritsu network analyser I have has 1M inputs and +20dBm input levels. With a 1:10 or 1:100 probe the input range can be extended.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline tggzzz

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #23 on: June 13, 2017, 07:02:17 am »
Tony,

Audio guy here, what do you need to test above 100k?  Or rather why?

Cheers,
Ruairi

I have been experimenting with wideband preamps, along with HF distortion caused by bandwidth limiting.

And no, I can't hear any difference before anybody asks!!

This is purely experimentation.

If your budget is limited, why not try some preliminary experiments with any old analogue scope? If nothing else, that will enable you to determine exactly what specifications you require for your tests.

If you are patient, you can find working 10MHz scopes on fleabay or gumtree for £10 - but make sure it is working! Or visit a local hackspace; my local one has so many of the damn things we are hoping members will take some before we tip them!
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Online nctnico

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Re: Please recommend a scope (or other device) purely for audio testing.
« Reply #24 on: June 13, 2017, 07:04:48 am »
@tggzzz: great, now tell him how to read data from an analog scope into a computer!  :palm:
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 


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