[Portaudio] loopback test is finding some bugs

[Phil Burk]

On 3/3/11 10:48 AM, Chris wrote:
> I now test for dropouts using a triangle wave instead of a sine wave, on
> the theory that any discontinuity in the test signal will be more
> apparent with a triangle wave due to the sine wave's smoothness at peaks
> and valleys, particularly at low frequencies.

That's a nice idea.

Do you have trouble with ringing at the triangle peaks? Since I am doing 
loopback I am worried that the antialiasing filters will distort the 
waveform. But a sinewave will pass mostly unmodified through the audio 
hardware.

The sine wave is nice because I can correlate with a sine+cosine pair. 
Using the phase results I can detect dropouts as small as one sample. I 
can also use a notch filter to remove the sine wave and measure residual 
noise or pops. Sine waves are pretty handy.

Phil