Comment by mikewarot

That's certainly handy... here's a simple audio frequency shifter I threw together[1].

First it takes the audio from your microphone. It then feeds it through a Hilbert transform to convert incoming audio into an IQ (complex) format. The advantage of an IQ signal format is that when you multiply it by another signal, the frequencies add or subtract, without getting extra image frequencies. This is why it's worth doing twice the computation in DSP work.

Then your audio is multiplied by a cosine wave with a frequency determined by a GUI slider, from -2000 to 2000 Hz.

This has the net effect of raising or lowering the pitch of your voice, like tuning in a single sideband transmission on ham radio.

To get the results out to the speakers, it samples only the real component to send to the audio output.

The net effect is it can raise or lower the frequency of your voice.

[1] https://gnuradioworld.com/#fg=H4sIAAAAAAAACsVXS2_bOBC--1fMTR...