Overlay audio tracks like layers are overlayed in photoshop

In photoshop you can choose to overlay images in different ways, so the the images interact and effect one another indifferent way (for instance you can ‘darken’, ‘lighten’, ‘multiply’. ‘difference’ etc.).

I was wondering if there were any different ways of overlaying/mixing sound that were conceptually comparable? I have tried AM modulation (which didn’t work that well, but removing the carrier wave was quite interesting) and I haven’t been able to find an FM equivalent bit of Nyquist code but it must be possible, and there must be other interesting ways to take 2 waves and mix them together so you don’t just get a literal mixing of the 2 (so that one changes the other in unexpected ways).

Can anybody help with this please?



Effect > Vocoder is a multiplier.



Peter Frampton’s [u]Talk Box[/u] is not a Vocoder. It’s a small mid-range speaker that leads the guitar sound over a plasic tube back into the mouth, where it is modulated by the motion of the oral cavity and then recorded by a microphone. A [u]Vocoder[/u] is an electric machine, a very early form of speech data compression developed for telephony, later used by musicians for voice effects.

@gshapely: Of course you can do all sorts of transformations to a sound, not only normal “mixing” by adding volume levels. The main problem is that because sampled sounds are nothing but series of more-or-less unrelated numbers, 99% of these transformations have not very meaningful results. Most of them produce nothing but distortion or noise.

Examples of numerical transformations with meaningful results:

  • Highpass filters are based on numerical differentiation, mixed back to the original sound.
  • Lowpass filters are based on numerical integration, mixed back to the original sound.
  • Bandpass and Notch filters are combinations of Highpass and Lowpass filters.
  • AM (amplitude modulation) and FM (frequency modulation) are based on multiplication of sounds.

A Vocoder is a combination of Bandpass filters (differentiation, integration) and Amplitude Modulation (multiplication).

Google for “The Computer Music Tutorial” by Curtis Roads (with John Strawn, Curtis Abbott, John Gordon, and Philip Greenspun). It’s the biggest collection of things you can do with sound, written for musicians (not primarily for technicians).

The Audacity “Effect > Nyquist Prompt” lets you play with nearly all transformations available for sounds. Starting from simple addition, subtraction, multiplication, division, up to all sorts of predefined oscillators and filters.

“Tremolo” is amplitude modulation (with a slow modulation frequency)
“Vibrato” is frequency modulation (with a slow modulation frequency). See here for a simple Nyquist example: https://forum.audacityteam.org/t/vibrato/18944/1
There is also “ring modulation” http://en.wikipedia.org/wiki/Ring_modulation
Ring Modulation can be achieved in Nyquist by multiplying two signals together (but watch out for aliasing)