# Is there anyway I can make spectrally deprived speech signal in Audacity?

I was researching about implants on the net and I came across this audio technique called spectrally deprived speech signal, which is how people with cochlear implant hear sounds from the implant. According to available information it can be produced by comb filter, by applying a signal to itself with a delay. So a signal with 1000 Hz information would be spectrally deprived by 950Hz, the remaining 50Hz could be vertically or horizontally spaced.

Is there anyway I can achieve this with Audacity?

There’s a comb filter provided in Nyquist.

From the Nyquist manual (http://www.cs.cmu.edu/~rbd/doc/nyquist/part8.html#index433)

comb(sound, decay, hz) > [SAL]
(comb sound decay hz) > [LISP]
Applies a comb filter to sound. A comb filter emphasizes (resonates at) frequencies that are multiples of a hz. The decay time of the resonance is given by decay. This is a variation on feedback-delay (see below). The hz parameter must be a number greater than zero. It is used to compute delay, which is then rounded to the nearest integer number of samples (so the frequency is not always exact. Higher sampling rates yield better delay resolution.) The decay may be a sound or a number. In either case, it must also be positive. (Implementation note: an exponentiation is needed to convert decay into the feedback parameter for feedback-delay, and exponentiation is typically more time-consuming than the filter operation itself. To get high performance, provide decay at a low sample rate.) The resulting sound will have the start time, sample rate, etc. of sound.

In practice, you can apply a Nyquist comb filter by entering this code into the Nyquist Prompt (https://manual.audacityteam.org/man/nyquist_prompt.html)
The first line tells Audacity that we will be using “version 4” syntax.
The next two lines set the “hz” (the root “resonance frequency”) and the “decay” (the decay time of the resonance).
In the final line, track is the selected audio.
The “scale” command scales the comb filtered sound by 0.2 to compensate for the boost produced by the comb filter.

``````;version 4
(setf hz 50)
(setf decay 2.0)
(scale 0.2 (comb *track* decay hz))
``````

Thanks