On Feb 5, 2017, at 12:54 PM, robert bristow-johnson wrote: > using the analytic filter to get the instantaneous amplitude envelope (and, > also, instantaneous frequency by differentiating phase) is something that > works only with single sinusoids that are AM'd or FM'd. for music, i think i > would LPF the square of the signal (or run an efficient sliding max > algorithm, we discussed this a while back) and work with that.
I'm curious what aspects of a music make the complex magnitude of the analytic signal inappropriate for estimating the envelope? In communications signal processing we use this often, even for signals that are fairly wide-band with respect to the sample rate and it seems to work. > but the reason i am most interested is in a frequency shifter. like the ham > radio single-sideband (SSB) thingie. this is not a pitch shifter and detunes > harmonic overtones into the inharmonic. but it is totally glitch-free and > can sometimes be handy to detune something slightly so that there is not a > buildup of energy at a specific frequency (when there is feedback of some > sort). pitch shifters can do that too, but time-domain pitch shifters might > have glitches for non-monotonic input and frequency-domain pitch shifters > have a huge throughput delay. also, this glitch-free frequency shifting can > be slowly modulated. might be useful for chorusing. combined with a pitch > shifter and pitch detector, you can shift harmonics without shifting the > fundamental (i.e. pitch it up with a pitch shifter and then bring back down > the fundamental to the original pitch.) Yes - the Bode-style frequency shifter is a fun and useful effect. I've done several of them for modular synthesizers using these IIR all-pass structures: With a dsPIC - http://www.modcan.com/bmodules/dualfs.html With an STM32F303 - http://modcan.com/emodules/dualfreqshifter.html Also with a dsPIC - http://synthtech.com/eurorack/E560/ There are example soundfiles at the above sites showing some of the subtle and radical variations that are possible with different amounts of shift, feedback and various shifting waveforms. Eric _______________________________________________ dupswapdrop: music-dsp mailing list music-dsp@music.columbia.edu https://lists.columbia.edu/mailman/listinfo/music-dsp
