[music-dsp] measuring partial frequencies

jeffrey traer bernstein jeffyb at ccrma.stanford.edu
Tue Jan 13 23:42:00 EST 2004


offline or realtime?
If it's offline then what's wrong with an FFT?

Peter Thom wrote:

>I don't understand what measuring frequencies has to do with wavetable
>synthesis.
>I don't want to generate sounds, I just want to be able to tell the
>frequency of the fundamental and it's partials.
>Initially I thought, it would be trivial, but it seems more complex than
>I thought.
>
>Peter
>
>
>
>
>-----Original Message-----
>From: music-dsp-admin at shoko.calarts.edu
>[mailto:music-dsp-admin at shoko.calarts.edu] On Behalf Of robert
>bristow-johnson
>Sent: Tuesday, January 13, 2004 2:52 PM
>To: music-dsp at shoko.calarts.edu
>Subject: Re: [music-dsp] measuring partial frequencies
>
>
>
>  
>
>>From: "Peter Thom" <peter at sonicreef.com>
>>To: <music-dsp at shoko.calarts.edu>
>>Subject: RE: [music-dsp] measuring partial frequencies
>>Date: Tue, 13 Jan 2004 10:26:55 -0800
>>Reply-To: music-dsp at ceait.calarts.edu
>>    
>>
>
>On 01/13/2004 10:26:55 -0800, Peter Thom at <peter at sonicreef.com> wrote:
>  
>
>>Yeah, I'm looking for frequencies other than the fundamental. FFT 
>>isn't accurate enough, I want to measure frequencies within 0.01Hz.
>>    
>>
>
>then, in my opinion, you want to seriously look at that Wavetable
>Synthesis paper (and remember "true" or classic wavetable synthesis is
>not the same thing as sampling "synthesis" which really isn't synthesis
>at all).  a frequency deviation of 0.01 Hz is essentially a slow
>changing of phase.
>
>  
>
>>Would a bandpass filter and zero crossing counting do, or is that not 
>>accurate enough? How about autocorrelation?
>>    
>>
>
>you might use something like that to precisely measure the period of a
>tone (which is useful for "pitch detection" or measuring f0), but it
>does not separate the partials which you will need to do somehow.
>
>  
>
>>BTW, the tone is a piano tone, so it should be a relatively periodic 
>>tone.
>>    
>>
>
>really, Peter, i don't know how deeply you want to dive into the math
>(the paper was done that way, with continuous-time, because it was the
>easiest way to be rigorous), but conceptually it is *not* that bad.
>
>in terms of implementation, i presume these piano tones are WAV or AIFF
>files, right?  and you have the means to open and parse them, right?
>what language are you planning to do this in?  C?  Matlab?
>
>  
>
>>Any help is greatly appreciated.
>>    
>>
>
>besides the means to put your sound file into an array of PCM data that
>you can do math on, you will need:
>
>    1.  a good pitch detection and pitch *riding* algorithm
>(autocorrelation
>        might work, but i think ASDF will work a little better).  this
>        algorithm also needs to measure how periodic the tone is at some
>        time within it so that you know when you crawled over the
>initial
>        transient or "attack" portion into the quasi-periodic portion.
>
>    2.  a good intersample interpolation utility.
>
>    3.  a DFT or FFT utility.
>
>    4.  lotsa memory, which shouldn't be a problem nowadays.
>
>what comes out will be a collection of phase-aligned, single period,
>wavetables and after FFTing them, you will have the instantaneous
>amplitude and instantaneous phase of each harmonic for that wavetable
>snapshot.  if the phase changes in time, that means the harmonic is
>actually detuned away from its exact integer multiple of the
>fundamental.  so if you know the fundamental frequency (from the pitch
>detector), the index number of the harmonic (from the bin number of the
>FFT), and the rate of change of phase (from comparing the phase of some
>particular harmonic of two neighboring wavetables), you have all of the
>information for a precise measurement of the instantaneous frequency of
>the harmonic.
>
>r b-j
>
>
>dupswapdrop -- the music-dsp mailing list and website: 
>subscription info, FAQ, source code archive, list archive, book reviews,
>dsp links 
>http://shoko.calarts.edu/musicdsp 
>http://ceait.calarts.edu/mailman/listinfo/music-dsp
>
>dupswapdrop -- the music-dsp mailing list and website: 
>subscription info, FAQ, source code archive, list archive, book reviews, dsp links 
>http://shoko.calarts.edu/musicdsp 
>http://ceait.calarts.edu/mailman/listinfo/music-dsp
>  
>




More information about the music-dsp mailing list