[LAD] Determining Phase

Jörn Nettingsmeier nettings at folkwang-hochschule.de
Sat Jun 25 15:57:08 UTC 2011

On 06/25/2011 04:23 PM, pshirkey at boosthardware.com wrote:
> Hi,
> Can anyone point me to a simple code example for how to determine the
> phase at a specific time in a waveform?
> ex. if I have a sample that is 5 seconds long and want to know the phase
> at 2.5 seconds

talking about the "phase" at some particular point in time doesn't make 
sense. first you would have to do an fft (whose resolution is bound by 
the window size), and then you'd have to look at each frequency bin 
separately, because they will all be at different relative phase.

when you talk directly into my ear, the voice/ear system will be roughly 
zero phase. when i move away even a few inches, there will be a linear 
phase "distortion" due to the fact that i'm now one wavelength away at 
some mid frequency, but several wavelengths at high frequencies.

so "phase" is not really a meaningful thing unless you are talking about 
recombination of strongly correlated signals.

another example: if your sample consists of a sine at 100hz and one at 
200hz, after 10ms the first component will be at 0° while the second is 
at 180°, iff both started at 0° in the first place. but why would anyone 
care? with real-life sounds, this whole exercise becomes meaningless.

what are you trying to accomplish?

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