What's a good technique to unit test digial audio generation

Question

I want to unit test a signal generator - let's say it generates a simple sine wave, or does frequency modulation of a signal onto a sine wave. It's easy enough to define sensible test parameters, and it's well known what the output should "look like" - but this is quite hard to test.

I could do (eg) a frequency analysis on the output and check that, check the maximum amplitude etc, but a) this will make the test code significantly more complicated than the code it's testing and b) doesn't fully test the shape of the output.

Is there an established way to do this?

Answer 1

One way to do this would be to capture a "known good" output and compare bit-for-bit against that. As long as your algorithm is deterministic you should get the same output every time. You might have to recalibrate it occasionally if anything changes, but at least you'll know if it does change at all.

Answer 2

This situation is a strong argument for a modeling tool like Matlab, to generate and review a well understood test set automatically, as well as to provide an environment for automatic comparison and scoring. Especially for instances where combinatorial explosions of test variations take place, automation makes it possible and straight forward generate a huge dataset, locate problems, and pare back if needed to a representative qualification test set.

Often undervalued is the means to generate a large, extensive tests exercising both the requirements and the limits of the implementation of your design. Thinking about and designing those cases up front is also a huge advantage in introducing a clean, problem free system.