toronz / audio_distortion

Measure the THD+Noise for your default audio device.

audio_distortion

A basic utility to measure the THD+Noise for your default audio device with a 1kHz tone. By default it generates and cptures 12000 samples @ 48kS/s (0.25s)

Creates a PPM image of the captured spectrum.

NOTE - only meausures the LEFT channel of the DEFAULT ALSA audio device.

WARNING: IF YOU SEND THE OUTPUT OF THIS PROGRAM TO YOUR SPEAKERS OR HEADPHONES YOU MIGHT DAMGAGE EITHER YOUR SPEAKERS OUR YOUR EARS

Prerequeists

You will need to have the ALSA dev libraries installed.

Using this program

1. Build with "make".

2. Attach a cable between line out to line in. Use a stereo cable.

3. Run ../audio_distortion <master volume %> <capture volume %>

4. On my system I get the best numbers from "./audio_destortion 90 9".

NOTE: Something is up with the capture volume - the driver reports different max an d min values than it seems to use. This may also be a bug.

5. Numbers will be displayed, and "graph.ppm" will be written.

Look in main() to change the test frequency

Optimizing the result for best numbers

If you have very high THD numbers (> 1%) you are either overdriving the output or input. Try reducing the capture volume, and if that doesn't help, also try reducing the master volume. A reasonable sound card should easily get well below 0.1%

Example output:

$ /audio_distortion 95 9
Audio playback device opened successfully.
Audio device parameters have been set successfully.
Init: Buffer size = 16384 frames.
Init: Significant bits for linear samples = 16
Audio device has been prepared for use.
Audio playback device opened successfully.
Audio capture device parameters have been set successfully.
Init: Buffer size = 16384 frames.
Init: Significant bits for linear samples = 16
Audio capture device has been prepared for use.
Setting playback volume to 62259 in range 65536 0
Setting capture level to 5898 in range 65536 0
Audio devices has been uninitialized.

Analysing captured data...

signal =   23365.16
dc     =      -0.05
thd+n  =       1.15  (  0.005%)
s:n    =      86.13 dB