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The phase of frequencies is very important to the final signal produced. A simple example would be two sinusoidal waves, at an interval of a perfect 5th. (Frequency ratio 1:1.5) Depending on the phase of the underlying sinusoids, the produced signal looks noticeably different.

One possible shape of a perfect 5th interval

Another possible shape of a perfect 5th interval

I understand that instruments are much more complicated than sinusoid generators as they produce an overtone series along with the fundemental frequency. The propogation of sound waves along with interactions from different types of instruments further complicates the issue. As is pointed out in another question, the phase of the signal produced is constantly changing due to all of the above factors.

However, when two instruments play a chord, it always "sounds" the same, as long as the underlying notes being played are kept constant. So what is this "average" chord that we are hearing and how do we calculate it?

YEp d
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  • I don't know where the notion comes from that it doesn't affect music. In settings with more than one sound source phase is extremely important and extremely audible. Many sound effects rely on the manipulation of phase (phasers, flangers, delays, echos are all phase related effects) and musicians/singers who are playing/singing "unison" are using phase to achieve strong effects. It's one of the reasons why choirs and large symphony orchestras sound much better than individual singers and instruments. – FlatterMann Jun 18 '23 at 06:55
  • @FlatterMann is it possible for musicians to even control the phase of the music they are producing? Phase does have a huge influence on music, but how can musicians actually manipulate it? – YEp d Jun 18 '23 at 07:06
  • Musicians can hear the interference and adjust the phase accordingly. In practice it is not done that way, though, at least not intentionally. Small frequency differences produce the same effect as a slow phase modulation. In electronical effects we have direct control over the phase of signals with delay and RC-ladder filters. – FlatterMann Jun 18 '23 at 07:11
  • @FlatterMann I see, thank you for your answer. I know the difference between electronic and "analog" music. What do you mean by small frequency differences produce the same effect as slow phase modulation? – YEp d Jun 18 '23 at 07:24
  • Two sine waves of almost identical frequency look very similar on a short time scale. On a longer time scale the delay between their zeros/maxima/minima will be a linear function of time, i.e. we can approximate such a linear phase variation with a slight frequency offset. – FlatterMann Jun 18 '23 at 07:28
  • @FlatterMann I see, that is a great explanation. – YEp d Jun 18 '23 at 08:08

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