The late analog design expert Robert "Bob" Pease wasn't known for mincing words. If the subject had anything to do with analog it's likely he had something to say about it, and that included many things audio.
For example, audio-related topics were often the focus of his column at Electronic Design, which he wrote for over 20 years:
Pease also authored a variety of application notes during his 33 years at National Semiconductor. The application note on which the above-listed column on output impedance was based is available at National's site:
The Effect of Heavy Loads on the Accuracy and Linearity of Operational Amplifier Circuits (PDF)
Finally, Paul Rako on his analog blog at EDN recounted details of a 2006 AES presentation in which Pease discussed his tests of audio capacitors, as well as test circuits that he used for measuring gain and distortion:
Bob had heard that the golden-ears audio crowd insisted that there was an audible difference between electrolytic and film capacitors when they were used in the audio signal path. Bob thought this was highly doubtful so he set out to measure the difference between several high-end audio capacitors. Turns out the golden ears guys were right and Bob is the first to admit that he can see a clear difference on the cross-plots put out by his favorite analog scope.
Read Paul Rako's complete blog post on Pease's AES presentation at EDN.