[sdiy] Better testing techiques for audio circuits

[Harry Bissell]

depends on what you are building... if its a fuzzbox than usual audio analysis instruments are pretty useless.

There are instruments (audio analyzer) that can give you the THD numbers etc. They make sense for amplifiers and
probably tone control circuits. They work (usually) by inputting a sine wave of known frequency, then notch filtering
the output at that same frequency, and measuring the result (which is THD, plus noise)

Your ears and you scope are a good first choice... unless you need to prove how good your circuit really is.

H^) harry

----- Original Message -----
From: Justin Owen <juzowen at gmail.com>
To: SDIY List <synth-diy at dropmix.xs4all.nl>
Sent: Mon, 02 Apr 2012 11:45:01 -0400 (EDT)
Subject: [sdiy] Better testing techiques for audio circuits

I'm after some general information on learning/developing better techniques for testing audio circuits.

For now, my main priority is to compare the quality of the input signal with the 'dry' (unaffected) output signal so I can see what effect (if any) the circuit is having on the signal.

One example of this might be putting a sine wave through a VCA to ensure that when the VCA was fully open - there was no change between input and output (or to see what parts were contributing to noise, distortion, etc.).

At the moment I switch between using a Sine Wave and a Square Wave and I compare the input and output signals visually on a scope...

...but if I wanted to get deeper than that - what should I be considering, researching, building or buying?

Another example - my mixer specifications tell me it has <0.0007 THD. How is this measured?

Would learning more about FFT help?

I'd appreciate some advice on this - no matter how general.

Thanks!

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-- 
Harry Bissell & Nora Abdullah 4eva