Ideal oscilloscope for audio applications (FFT and FRA)

[Thomas_B]

Hello everybody,

I'm a long-time reader of this forum, but now I'd like to ask for your advice.

I don't have an oscilloscope yet, but a good multimeter as my only measuring instrument. Since I want to address the construction of analog synthesizer modules, I can't get around the purchase of a suitable scope. My first project is a 24dB filter with voltage-controlled frequency and resonance. I've read several threads on entry-level scopes (and the "Digital Oscilloscope Chart" of course), but haven't found the ideal model for me.

The device should fulfill the following points:

• Future-proof bandwidth, sample rate, and record length: Here I lack the experience to estimate how a scope should be dimensioned so that the device is sufficient even with growing tasks.
• Proper FFT analysis functions: I'm aware that an oscilloscope can't replace a dedicated FFT spectrum analyzer. In order to analyze the filter behavior and saturation effects, the device should still have a decent FFT function with lots of measurement points and good usability.
• Frequency response analysis (Bode plots): I know this is a relatively new feature for oscilloscopes, but I think it would be very useful for designing (variable) filters. Therefore, in my preselection, I have included only models that have this feature.

With these specifications in mind, I've selected the attached models.

On paper, the Siglent SDS2202X-E looks like a clear winner, but the device is pretty new (means buggy?). In addition to the SDS1202X-E I found two videos that show signal distortions at low frequencies:
https://youtu.be/Vmbyodjs7cE?t=1459
https://youtu.be/mShWlCt2ARw?t=614

The low-frequency range is definitely relevant for my application. I wouldn't like to compromise here.

I would be glad if you could give me some advice on the mentioned models or could possibly give me alternatives that meet the desired requirements.



Thank you and cheers!
Thomas

[bd139]

I wouldn't bother with a scope for that work.

Have a look at this: https://reference.digilentinc.com/reference/instrumentation/analog-discovery-2/start

2x 14 bit scope channels
2x 14 bit AWGs
Impedance and spectrum analyser.

You can't look at audio distortion easily in the time domain on a scope. You'd need a frequency domain instrument for that which the above provides.

A decent pro audio sound card and some attenuators also act as a better instrument for audio now.

[tggzzz]

I'll second bd139's comments.

I'll add that if you become seriously interested in this area, you might need a professional "audio analyser". Secondhand ones are available on fleabay and elsewhere, with the obvious possible disadvantages.

[frozenfrogz]

For purely audio applications, get a decent audio interface and do everything else in software on an OS X / Windows or Linux machine.

[Thomas_B]

Thank you for your fast response.
I'll take a closer look at the Analog Discovery device. However, I'd like to have a scope that works without a laptop/desktop PC.

I already own a reasonable audio interface (Presonus Studio 68). Due to the AC coupling, I can watch audio signals, but no control voltages (like LFOs and envelope curves) on the computer. I've used software scopes and spectrum analyzers like s(M)exoscope and Voxengo SPAN. But with my interface, this solution is limited to around 15 Hz and up. Therefore, my audio interface complements my project, but can't take over all tasks.

[nctnico]

Instead of the GW Instek MDO2000E series I'd get the MSO2000E series and use a keygen to add the spectrum analysis mode (and while you are at it, you can also unlock these oscilloscopes to a bandwidth of 300MHz on 2 channels). Still for audio I think the 10 bit RTB2k is in a class of it's own.

[tautech]

On paper, the Siglent SDS2202X-E looks like a clear winner, but the device is pretty new (means buggy?). In addition to the SDS1202X-E I found two videos that show signal distortions at low frequencies:
https://youtu.be/Vmbyodjs7cE?t=1459
https://youtu.be/mShWlCt2ARw?t=614

The low-frequency range is definitely relevant for my application. I wouldn't like to compromise here.

Welcome aboard Thomas.

A couple of comments
Be wary of the info portrayed in old videos as the later SW developments and even factory HW revisions can make historical issues obsolete. SDS1202X-E don't have any issues like that today and are my best seller.

FYI there has been a recent big FW release for SDS2202X-E and you can see what was addressed here:
https://www.siglenteu.com/wp-content/uploads/dlm_uploads/2019/09/sds2000x-e-firmware-revise-history-and-update-instructions.pdf

I too like the SDS2202X-E and more so its bigger brother SDS2352X-E. Both are a nice step above SDS1202X-E capabilities.
Nice DSO's and if there's anything you'd like a screenshot of please let me know.

[rsjsouza]

I know you are looking for a standalone unit, but, as others have said, the resolution of bench oscilloscopes will not be as good for audio.

Just adding a bit more noise to the mix, there is also the option of a Picoscope 4262, which is a 5MHz 16 bit PC-based oscilloscope that also features a reasonable arbitrary waveform generator. It is an expensive unit when compared to the models here, but quite decent for audio. Its software is praised by some that are familiar with it (I've been eyeing one but so far my better half disagrees with the expenditure...)

[Muxr]

That picoscope is interesting. But for the same price you can get a dedicated standalone scope and a SignalHound SA44B which goes all the way down to 1hz. Which in my opinion would be a much more capable solution, beyond just audio.

[egonotto]

Hello (Servus),

the Picoscope 4262 is very very nice with very low noise, but only for low frequency ( <1MHz) and if you have no wife .

Perhaps the following makes sense:
Siglent SDS1104X-E    510.51€ (Batronix)
Siglent SDG1032X       308.21€ (Batronix)
Analog Discovery         269    €  (akademisch nur 193 falls Student) (Trenz)

The Analog Discovery is a little lab and very nice to have.
But under +-2.5V it use digital zoom so you lose bits

Is the 24dB filter with OTA's perhaps from Doepfer?
 
Best regards
egonotto


 

[Fungus]

I know you are looking for a standalone unit, but, as others have said, the resolution of bench oscilloscopes will not be as good for audio.

This. Those 8-bit samples just don't cut it for fine audio.

A 'scope with (eg.) 12-bit sampling will cost a lot of money so my suggestion is to bite the bullet and go for a PC-based solution. I know you don't want to, but that's the way it is.

You can buy an Analog Discovery (14-bit samples), a cute little laptop to connect it to, a cheap oscilloscope for your other "oscilloscope" needs, and spend a lot less money than "Ideal oscilloscope" (plus maybe signal generator).

[n3mmr]

As always: if you're serious you buy a Quantasylum QA401 and run the included SW.
You need a tiny Windows 10 PC and a good screen. The PC can be the 200 dollar fanless types.

QA401 works very close to 24bits resolution and most calculations run inside the QA401,in an fpga.
Cost is in the same range as an sds1104x-e.

[Thomas_B]

Thank you for the many suggestions. I've watched a few videos about Analog Discovery 2 and that looks promising and I can imagine that the combination with a (cheap) stand-alone device could be the way to go. But I don't want to work exclusively on the laptop. After all, I'd like to work on that project in my spare time, and I try to avoid PCs...

That picoscope is interesting. But for the same price you can get a dedicated standalone scope and a SignalHound SA44B which goes all the way down to 1hz. Which in my opinion would be a much more capable solution, beyond just audio.

The spectrum analyzer from Signal Hound looks great, but it's definitely beyond the budget since I still need an additional scope here.

Is the 24dB filter with OTA's perhaps from Doepfer?

I haven't thought about the exact filter design, probably it will be some kind of Moog-ish clone (transistor ladder, not an OTA) . From Doepfer I own only an ADSR envelope generator (A-141-2) and my two cases.

I know you are looking for a standalone unit, but, as others have said, the resolution of bench oscilloscopes will not be as good for audio.

I'm not worried about the vertical resolution of 8 bits. For acoustic tuning, I can still rely on my audio interface with 24-bit converters.

As always: if you're serious you buy a Quantasylum QA401 and run the included SW.

That thing looks great. I'll check that out.

[SWR]

Hi Thomas

I've got the MDO-2204EX purchased from Reichelt in Germany.
I'm very satisfied with the FFT and Bode plot performance.
It's high resolution combined with a fast update rate.
I really like the spectrum analyzer type user interface, where you don't have to fiddle with time domain sampling rates to zoom into an area of interest.

I also have a Siglent spectrum analyzer with much higher dynamic range, but it bottoms out at 9KHz, so it's not usable for audio.

I chose the EX because it has DMM and dual PSU integrated, but be aware that the PSU only goes to 5V, so I don't think it will be of much use for audio.
I mainly fiddle with IoT modules.

Best regards
Soren

[harha]

Hi
Try look at a soundcard solution---like spectraplus..tlf 29281995
Hardy

[james_s]

A friend of mine does some similar work, he uses an old HP audio spectrum analyzer from the 1970s, it goes up to about 50kHz and is perfect for this sort of thing. I don't know the model offhand but I don't think he paid very much for it.

[DaJMasta]

A friend of mine does some similar work, he uses an old HP audio spectrum analyzer from the 1970s, it goes up to about 50kHz and is perfect for this sort of thing. I don't know the model offhand but I don't think he paid very much for it.

It's a dynamic signal analyzer, purpose designed for sound and vibration testing, but they've basically been discontinued given the availability of audio analyzers on the high end and simple sound cards on the low, so you can find older ones for fairly cheap, but there's few new direct comparison products.

If you don't have a scope then getting one is probably a higher priority than measurement resolution/noise floor - it's a versatile tool that will be widely applicable beyond this application.  That said, if you're sticking to audio frequencies, you may be fine off with a decent PC sound card (USB, often) and some measurement software.  If you want high resolution, low noise audio equipment, a lot of dedicated equipment for it will be very, very overkill, and performance of even a decent sound card will probably be better in the audio band (probably 16+ effective bits) than most scopes or similar.  Now a conventional sound card will be limited in measurement range, may not be well referenced for absolute measurements, and doesn't have the input/output protection test equipment usually provides, but it could be a free plus whatever software you choose option to accompany and augment your scope purchase.

[Old Printer]

TomTekTest on YouTube has done some videos on audio testing with the Analog Discovery. He used some audio analyzer software written by someone else that was supposed to be very good. Maybe not on a professional level, but from what i read certainly worth looking at. The author is apparently very knowledgeable, but he had some hosting issues and dropped of the radar for a while. Last I saw, about a year ago, he had them taken care of and his site was back up and he was working on some new additions as well.

[graybeard]

The best spectrum analyzer for audio use is ARTA.  It uses you computer sound card and will do 24 bits at 192 KHz sample rate if your sound card is capable.  It hass built in distortion measurements and uses the sound card output as a coupled signal source.  It can also act as a ac coupled oscilloscope with up to 24 bit resolution, measure frequency response, and be used to measure impedance with some external circuitry.

I run it using WINE on Mint Linux and it works great.

It is free to use so long as you don't want to save data.   It is 79 Euros ($87.50 at today's exchange rate) to get the full version.

[Old Printer]

A little OT here but from a hobbyist perspective, what would you do with this sort of hardware/software? I play some guitar, tinker with tube amps and some pedals and have a good interest in music and home hifi in general. Since i have most of the equipment to do this a few ways, I am curious what to do with it. Thanks.

[drknob]

This one is free:
http://www.sillanumsoft.org/prod01.htm

[GerryR]

A little late to the party, but you might want to take a look at:  https://www.virtins.com/VT-DSO-2820.shtml for a PC solution.  If nothing else, you might want to download some of their .pdf's  from their applications page, just for the education: https://www.virtins.com/applications.shtml