[sdiy] Vocoder dabblings

Mattias Rickardsson mr at analogue.org
Sat Oct 27 01:24:38 CEST 2012


Very good! :-)

/mr

On 21 October 2012 22:32, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
> Hi guys and girls,
>
> Been playing about with coding up a Vocoder just for fun after recently
> having to design a filter bank for a commercial job.  Have included a few
> audio examples of the results I'm getting for those interested:
>
> http://www.richieburnett.co.uk/temp/vocoder1.mp3
> http://www.richieburnett.co.uk/temp/vocoder2.mp3
> http://www.richieburnett.co.uk/temp/vocoder3.mp3
> http://www.richieburnett.co.uk/temp/vocoder4.mp3
> http://www.richieburnett.co.uk/temp/vocoder5.mp3
> http://www.richieburnett.co.uk/temp/vocoder6.mp3
> http://www.richieburnett.co.uk/temp/vocoder7.mp3
> http://www.richieburnett.co.uk/temp/vocoder8.mp3
>
> Technical specs as follows:
>
> Processor is dsPIC30F6012A 16-bit DSC from Microchip running at 25MHz. Audio
> sample rate is 24kHz.  Vocoder is 20 bands (20 analysis + 20 synthesis),
> each 1/3rd octave, filters are 8th order Butterworth band-pass response
> (24dB/oct slope each side)  (160 seperate state-variable filters in total!)
> Lowest band is 60Hz, highest band is 6kHz, although the bands in the lowest
> octave do little with speech signals.  Sibilance from modulator above 6kHz
> is high-pass filtered and mixed in with the modulated carrier to increase
> intelligibility.  +3dB/oct spectral tilt is added for classic
> sawtooth/square based carriers, and -3dB/oct spectral tilt is added for
> white noise carrier.  No user-interface or spectral display.
>
> Modulator audio was either Radio-4 news, or audio sample played from Akai
> sampler.  Carriers are various waveforms or white noise from Roland SH-09,
> or hoover sound from Juno-2.
>
> Never built a vocoder before, either analog or digital so please be kind...
>
> -Richie,
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