I want to linearly shift the frequency of a clip by 100 Hz lets say.
So 1000 Hz would shift to 1100 Hz
And 500 Hz would shift to 600 Hz.
I would also like to be able to slide this, (change the amount of frequency shift over time) but that would probably make it even more complicated.
Is this possible to do in Audacity? I don’t Know NYQUIST, so I would greatly appreciate any help.
What I am trying to simulate is a Single Sideband Communications receiver off frequency by a little bit.
If the track is resampled to a high sample rate (for example 192000 Hz), then we can model that process using a few Nyquist commands in the Nyquist Prompt effect (http://manual.audacityteam.org/man/nyquist_prompt.html)
; first, bandpass the audio
(setf sig (highpass8 (lowpass8 *track* 8000) 100))
; then amplitude modulate.
; The carrier frequency must be substantially higer than
; the band limited signal.
; we're also adding a fixed gain of 8x
(setf am (mult sig 8.0 (hzosc 40000)))
; notch filter to remove carrier
(setf am (notch2 am 40000 20.0))
; ultra-steep low pass filter to remove upper side band
(dotimes (i 12)
(setf am (lowpass8 am 39900)))
; using a demodulation frequency 200 Hz higher
; than the original carrier, and
; low pass our band limited audio
; and add 2x gain
(lowpass8 (mult 2.0 am (hzosc 40200)) 8000)