Re: [linux-audio-dev] the bandwidth of the each harmonic

--- Christian Schoenebeck <schoenebeck(a)software-engineering.org> wrote: "Should" :) Because the natural ensembles have this tendency (the individual instruments's are very like to be somehow uncorelated. Ex: you cannot synchronize 2 singer that plays same note to start at same phase of the fundamental note). So, I belive that the ensembles sounds beautifull because the bandwidth of each harmonics as described earlier AND the phases are random (uncorelated). Also, another thing that adds randomness to the harmonic phases is the reverberation. Think for example, one singer plays a note for few seconds: of course he cannot keep the same note, and will result a slight vibratto, that is a the simplest way to make the bandwidth of each harmonic as described before. Or good singers know how to add vibratto to their voices. The problem is that there is a certain relationship between the frequencies of a certain harmonic (in order to result a "frequency modulated" sound by a very low frequency). But if you pass this sound into a reverbation, the phase relationship will be "destroyed" and will result random phases on the frequencies contained in the frequency band. I noticed that the better is the reverberation, the more randomness is added to the phases of the wet reverb signal. To intuitively demonstrate this (that a good reverb makes the phases more random), let's consider a very ugly reverb: a simple comb echo with little delay(say 50 ms) with a very high feedback. This "reverb" sounds awful, in most cases. If you draw the phase response of this, you'll see that this filter changes the phases of the incoming signal by a not random (or pseudo-random) matter. Of course, if you add 2 or more comb filters, and the delay are uncorelated, will be more likely to add a random phase to the signal and this makes that the phases of the incoming signal to be more likely to be random. I attached 2 files (for zynaddsubfx) to explain more about above: 1) bw_without_randomness.xmz This makes bandwidth of each harmonic by the simplest way: it adds a vibratto to the sound. I am reffering as "bandwidth" and not "fast changing the pitch according to the time", because I am consider sound from the perspective of long FFTs. You see that is not well sounding, because even if it has bandwidth, but it lacks randomness of the phases. 2) bw_with_randomness.xms I added the randomness, using a reverb and taking only the wet signal. You see, that it sound very good, even like a very big ensseble, but because the reverb, the sound last few seconds more than the first. Another way that I can convert from the first sound to the second, is to sample few seconds from the sound, do a long term FFT (in fact the whole sound :) ), make the phases random and than, do a IFFT. Another important thing that I noticed, regarding FFT's and random phases, is the IFFT of a signal with random phases is periodic (you know this about the periodicity of the FFTs...), and this helped me alot to design PADsynth algorithm; because I know that the IFFT is smoothly periodic,so I can easily loop the sample w/o any clicks or artifacts regarding loops. Paul http://zynaddsubfx.sourceforge.net __________________________________ Do you Yahoo!? Meet the all-new My Yahoo! - Try it today! http://my.yahoo.com