[sdiy] Audio Spectrum Analyzer

[rsdio at audiobanshee.com]

The biggest problem with software solutions is that they’re only as good as the audio interface, and audio electronics are not nearly designed to the exacting standards of test and measurement equipment. You might think that high-end brands would be every bit as good as professional test equipment, but that’s not necessarily true.

I was working on a project which involved sine wave frequencies up to 50 kHz or 60 kHz, which is easily handled by 192 kHz audio equipment, or even less expensive 96 kHz audio equipment (just barely supports 48 kHz signals). It turns out that there was a great deal of noise around 16 kHz, which had everyone mystified. After years of working around that noise - and assuming that it was in our custom hardware - the test equipment was changed from RME brand to Metric Halo Labs. Suddenly, the 16 kHz noise was completely gone. This tells me that RME, although having a reputation for pristine audio quality, were doing something odd that made their circuits susceptible to this noise. I was never sure whether the noise was coming from the RME itself, or perhaps being conducted in by a ground or shield. Meanwhile, the MHLabs gear was better shielded or perhaps simply avoided paths for interference by clocks at those frequencies, and more importantly showed that there was not actually a problem in our custom hardware.

Anyway, my strong assumption is that a professional piece of gear like an oscilloscope with spectrum analysis, or a dedicated hardware spectrum analyzer, would not falsely show noise that was unrelated to the thing being tested.

Then again, despite the high price of something like an RME or MHLabs audio interface, the professional bench gear is way more expensive as well as being an order of magnitude more strictly designed to avoid unintended interference.

A good option to save money would be to find a product that puts the high-quality front end of an oscilloscope into a USB (Audio) Device that could pass the data to a Host computer for analysis. Like an audio interface, but designed for test and measurement. Then, you’d have the best of both worlds: no false results because the front end is appropriate for testing and measurement; and no crazy prices because the software portion can run on computers that you’ve already paid for.

I believe that there are a number of digital scope front ends on the market, and maybe even some that are macOS compatible (where I find the graphics to be much easier on the eye, akin to analog displays). I just haven’t had the time to evaluate these hybrid products. An ex-coworker of mine wanted to design such a front end, but his focus on steady employment got in the way of starting a new product venture. I still think it’s a great idea if someone hasn’t already aced the challenges.

Brian Willoughby


On Apr 6, 2018, at 7:07 AM, Tom Bugs <admin at bugbrand.co.uk> wrote:
> Interesting that, apart from this QA401 hardware/software team, everything suggested is software.
> 
> Not entirely surprising given the price and size of old hardware - I somehow picked up an HP35660A and an HP35665A and they are beasty massive.
> 
> On 05/04/2018 02:45, Jean-Pierre Desrochers wrote:
>> https://quantasylum.com/collections/frontpage/products/qa401-audio-analyzer
>> 
>> I have one and it's a FANTASTIC device !!!
>> JP
>> 
>> -----Message d'origine-----
>> De : Synth-diy de la part de Michael Zacherl
>> Envoyé : 4 avril 2018 19:38
>> À : synth-diy at synth-diy.org
>> Objet : Re: [sdiy] Audio Spectrum Analyzer
>> 
>> On 5 Apr 2018, at 00:05, John Marshall <wa7bsr at gmail.com> wrote:
>>> I am looking for an Audio Spectrum Analyzer. Which Audio Spectrum Analyzer do you use?
>> Despite its antique interface I like and used to use baudline.
>> But I just realised that it apparently didn’t survive the upgrade to macos 10.12.
>> It just won’t launch anymore.
>> 
>> However, have a look: http://www.baudline.com/download.html
>> HTH, m.