Please recommend a scope (or other device) purely for audio testing. - Page 1
Forum section: electronics / testgear

author: uktony
author_rank: Contributor
timestamp: June 12, 2017, 02:56:42 pm
content: 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 FRA4Picoscopehttps://bitbucket.org/hexamer/fra4picoscope/wiki/Hometo 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 AnalogueexplorerDiscovery 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 plottingDownloadable dataLinux compatibility would be nice (to enable scripted testing)An onboard DDS generatorUSB 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).

author: nctnico
author_rank: Super Contributor
timestamp: June 12, 2017, 03:11:55 pm
content: Digilent Analog discovery?

author: simone.pignatti
author_rank: Frequent Contributor
timestamp: June 12, 2017, 03:19:08 pm
content: the Pico 4262 is a good solution for audio testing, see the specs act pico website herehttps://www.picotech.com/oscilloscope/4262/picoscope-4262-specifications

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 12, 2017, 03:24:54 pm
content: 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.

author: uktony
author_rank: Contributor
timestamp: June 12, 2017, 03:32:46 pm
content: Quote from: nctnico on June 12, 2017, 03:11:55 pmThis is already on my list.Quote from: simone.pignatti on June 12, 2017, 03:19:08 pmNice, but way over my budget. My budget is max £300.Quote from: schmitt trigger on June 12, 2017, 03:24:54 pmAgain - way over my budget. I've seen these advertised for well over $2k on Ebay!!

author: ruairi
author_rank: Frequent Contributor
timestamp: June 12, 2017, 04:00:43 pm
content: Tony,Audio guy here, what do you need to test above 100k? Or rather why?Cheers,Ruairi

author: nctnico
author_rank: Super Contributor
timestamp: June 12, 2017, 04:08:12 pm
content: Quote from: uktony on June 12, 2017, 03:32:46 pmWith some patience a good deal can be found. Also asking prices on Ebay are usually way too high.

author: uktony
author_rank: Contributor
timestamp: June 12, 2017, 04:30:39 pm
content: Quote from: ruairi on June 12, 2017, 04:00:43 pmI 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.

author: DaJMasta
author_rank: Super Contributor
timestamp: June 12, 2017, 04:35:09 pm
content: +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 youreallyneed 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.

author: ruairi
author_rank: Frequent Contributor
timestamp: June 12, 2017, 05:20:46 pm
content: Quote from: uktony on June 12, 2017, 04:30:39 pmI'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.

author: Fungus
author_rank: Super Contributor
timestamp: June 12, 2017, 05:47:17 pm
content: Quote from: uktony on June 12, 2017, 04:30:39 pmWhy 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.

author: uktony
author_rank: Contributor
timestamp: June 12, 2017, 06:08:54 pm
content: Well I found what must be old stock of the Tsunami -https://www.crowdsupply.com/arachnid-labs/tsunamiWhich I'm hoping will do exactly what I want -https://github.com/arachnidlabs/tsunami-arduino/wiki/Measuring-Frequency-ResponseIt 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 seeexactlywhat my circuits are doing, regardless of total bandwidth - and this tool will just be a supplement to measurements made with PC software and Focusrite.

author: DaJMasta
author_rank: Super Contributor
timestamp: June 12, 2017, 06:58:29 pm
content: 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.

author: egonotto
author_rank: Super Contributor
timestamp: June 12, 2017, 07:23:40 pm
content: Hello,uktony wrote:"So what would I like:FFT / bode plottingDownloadable dataLinux compatibility would be nice (to enable scripted testing)An onboard DDS generatorUSB 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 regardsegonotto

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: June 12, 2017, 07:32:03 pm
content: for amplifier circuits for audio, whether op amp or discrete, stability verification requires 10s of MHz viewing BW at the least

author: David Hess
author_rank: Super Contributor
timestamp: June 12, 2017, 08:15:34 pm
content: I have never used them but Syscomp Design makes some instruments which may suit your needs.http://www.syscompdesign.com/Instruments_ep_42.html

author: nctnico
author_rank: Super Contributor
timestamp: June 12, 2017, 10:56:47 pm
content: 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.

author: Someone
author_rank: Super Contributor
timestamp: June 12, 2017, 11:17:50 pm
content: Quote from: egonotto on June 12, 2017, 07:23:40 pmThe 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.

author: ruairi
author_rank: Frequent Contributor
timestamp: June 13, 2017, 01:06:03 am
content: Quote from: nctnico on June 12, 2017, 10:56:47 pmThe 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.

author: Keicar
author_rank: Regular Contributor
timestamp: June 13, 2017, 01:55:37 am
content: Quote from: f5r5e5d on June 12, 2017, 07:32:03 pmAbsolutely - 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.

author: David Hess
author_rank: Super Contributor
timestamp: June 13, 2017, 02:41:40 am
content: Quote from: Keicar on June 13, 2017, 01:55:37 amThat 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.

author: mtdoc
author_rank: Super Contributor
timestamp: June 13, 2017, 03:25:12 am
content: The Digient Analog Discovery is likely perfect.12 bit scope with 30MHz bandwidth (using BNC adapter)10MHz AWGNetwork AnalyzerSoftware with Linux SDK available (I think)And check outthis thread on Jaxbird's excellent audio analysis sotware developed for it.

author: nctnico
author_rank: Super Contributor
timestamp: June 13, 2017, 06:37:20 am
content: Quote from: ruairi on June 13, 2017, 01:06:03 amThe 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.

author: tggzzz
author_rank: Super Contributor
timestamp: June 13, 2017, 07:02:17 am
content: Quote from: uktony on June 12, 2017, 04:30:39 pmIf 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!

author: nctnico
author_rank: Super Contributor
timestamp: June 13, 2017, 07:04:48 am
content: @tggzzz: great, now tell him how to read data from an analog scope into a computer!

author: uktony
author_rank: Contributor
timestamp: June 13, 2017, 08:32:54 am
content: Thanks for all the replies and just to add a few points:I already have a 30MHz Owon 'scopeI also have a Velleman PCSU200 'scope + waveform generator(lousy software)I am building preamps *not* power ampsI have a FocusRite Scarlett 2i2 (V2) USB interface (192kHz)I realise that the Tsunami device has it's limitations, however as a basic measuring tool I reckon it'll suit my purpose in this instance.I was looking for further insight into my measurements, as I've been finding that some of my designs show a rising response just at the top end of my sound card measurement ability ~85kHz which I though was odd (it's not the sound card or the measuring software).Finally - my Owon 'scope has an FFT function which isn't bad, however apart from basic screen grabs, accessing the data from a PC results in a .bin file which only the Owon software can read.

author: tggzzz
author_rank: Super Contributor
timestamp: June 13, 2017, 10:04:37 am
content: Quote from: nctnico on June 13, 2017, 07:04:48 amYou appear to have missed the word "preliminary". That may, or may not, be sufficient for his purposes.Personally I would think that if he is interested in audio signals, then looking at MHz signals is only beneficial as a sanity check to verify there's nothing stupid happening. An analogue scope might be sufficient for that.If not, then the Digilent Analog Discovery is probably a reasonable choice, but that is 10* more expensive and the OP has limited finances. I have no idea whether the AD would be sufficient for audiophile level testing.

author: Fungus
author_rank: Super Contributor
timestamp: June 13, 2017, 10:45:51 am
content: Quote from: tggzzz on June 13, 2017, 10:04:37 amIf you live in a place where they're easy to find for $25.Quote from: tggzzz on June 13, 2017, 10:04:37 amWill your analog 'scope do frequency sweeps and bode plots? That's what audio work needs and the AD will do that nicely (muchbetter than any 8-bit DSO).

author: uktony
author_rank: Contributor
timestamp: June 13, 2017, 12:38:56 pm
content: This is a screenshot of a 5Hz to 1MHz on my Owon 'scope.I enabled persistence to get a solid image.Unfortunately there's no logarithmic option that I can find.This sweep was generated by an AD9850 DDS generator that I control with an Arduino. I wrote a Windows program in vb.net to control it.

author: tggzzz
author_rank: Super Contributor
timestamp: June 13, 2017, 01:49:05 pm
content: Quote from: Fungus on June 13, 2017, 10:45:51 amI know West Yorkshire is "oop t'north", but it isn't that remoteThere are several available on gumtree and fleabay!QuoteWhile desirable, they might not benecessary. Given the OP can sweep a AD9850, he could generate a log frequency plot. Log amplitude would require a log amplifier.Is 14-bit sufficient for the OP's puposes? Audiophiles might think not.It is up to the OP to determine whatelsehe could do with any money saved (oops: not spent).

author: Fungus
author_rank: Super Contributor
timestamp: June 13, 2017, 02:33:28 pm
content: Quote from: tggzzz on June 13, 2017, 01:49:05 pmThe number of bits just sets the noise floor.The noise floor demanded by audiophiles isn't the same as the noise floor needed for a piece of test gear.

author: tggzzz
author_rank: Super Contributor
timestamp: June 13, 2017, 05:51:31 pm
content: Quote from: Fungus on June 13, 2017, 02:33:28 pmPlus, implicitly/indirectly, some other performance points, e.g. intermodulation and SFDR. Noise floor isn't the only parameter; see my .sig.QuoteWhich has the more stringent requirement depends on the tests being done and, in the case of audiophiles, the person

author: Fungus
author_rank: Super Contributor
timestamp: June 13, 2017, 05:55:37 pm
content: Quote from: tggzzz on June 13, 2017, 05:51:31 pmThat's why I used 'demanded' and 'needed'.

author: Loboscope
author_rank: Regular Contributor
timestamp: June 13, 2017, 08:59:17 pm
content: As everybody knows, audiophiles/audiophools are not interested in measurements and they will not make measurements. Because they have their "Golden Ears", and they are convinced, that these "Golden Ears" will even outperform the most recent Audio Precision gear so that ap will get jealous. Why bother about cost-intensive collected data of audio-gear when you have these "Golden Ears" and you will hear immediately the difference?Back to topic:As I wrote before in other posts I always recommend the software "hpw-works" [http://www.hpw-works.com/] for measuring audio-gear. Together with a good/professional interface/sound-card you will be able to determine any relevant technical data of your audio-gear, reliable and with high precision - of course within the frequency-limits of your interface.

author: Gary.M
author_rank: Regular Contributor
timestamp: June 13, 2017, 09:33:02 pm
content: Quote from: Loboscope on June 13, 2017, 08:59:17 pmStupid comments Lobo(Tomy)scope.The op needs an Analogue Discovery as others have said. Look for one on ebay. You can use the network Analyzer to do what you want. Open loop bode plots?Sent from my x600 using Tapatalk

author: Gary.M
author_rank: Regular Contributor
timestamp: June 13, 2017, 10:53:33 pm
content: Quote from: blueskull on June 13, 2017, 09:47:25 pmSoundcard based software won't do what the op said he wanted to do.Sent from my x600 using Tapatalk

author: uktony
author_rank: Contributor
timestamp: June 14, 2017, 07:44:31 am
content: Quote from: Gary.M on June 13, 2017, 10:53:33 pmIndeed - I already ahve RMAA PRO and Audiotester. I also use Realtime Analyzer from here ->http://www.ymec.com/products/app/ra2.htmAll of the above are good software, but are still limited by sound card bandwidth of course.HpW (very, very quirky and difficult to navigate) was evaluated, however that too would still be constrained by the limits of the sound card bandwidth.Finding a used Analogue Discovery has proven to be difficult, as I guess people don't part with them in a hurry (even the first version).The QA401 from QuantAsylum was also looked at, but again it's way over my budget.I started this thread with the idea that someone might suggest something I've never heard of, or perhaps even a method / device I had not even considered.But evidently I think I had considered all options!

author: uktony
author_rank: Contributor
timestamp: July 13, 2023, 09:33:49 am
content: I was recently reminded of this thread so thought I should update it.Six years later (six!) I have learnt a lot.The Tsunami device I mentioned in my earlier posts turned out to be quite useless. I guess I was expecting too much.A typical (affordable for a hobbyist!) digital scope is 8 bit or 12 bit, neither of which are much use for high resolution audiomeasurements.I purchased a used Handyscope HS3https://www.tiepie.com/en/usb-oscilloscope/handyscope-hs3from 'TiePie' which has a 16 bit resolution mode with limited bandwidth (up to 200kHz from memory).This has proven to be quite useful for tracking anomalies like oscillation etc.But for measuring THD, SINAD and various other parameters, one really needs 24 bit, which means using a PC with sound card.I purchased an Asus Xonar STX and using Wavespectra and Virtins Multi Instrument I am able to achieve some really useful measurements.I created a dedicated page for audio test and measurement on my website for those interested.https://gtkc.net/audio-test-and-measurement-for-diyI've attached a screenshot of a typical measurement.