[sdiy] vocoder design questions

[Paul Perry]

At 07:21 AM 23/03/03 -0800, you wrote:
>I am thinking about trying to design + build one of these.  My goal is to
>get the sort of sound a Bode 7702 has: to my ears, crisp, with good
>clarity and low distortion and noise.  Hopefully without the Bode 7702
>vintage sort of price.
>
You need:
"Vocoder Filter Design: Practical Considerations" Roger M Golden
Journal of the Acoustical Association of America v34 #4 1968 p 803-810

"Analysis of Filter Bank Transfer Functions" Milic, Kamsek & Jocic 
Proc IEEE v134 ptG #1 Feb 1987 p23-30

It would be a mistake not to reaad the first paper, which argues that 
1. you want Bessel
2. sometimes you want to alternate the phase of adjacent channels

In general, the filters are not equal bandwith & I doubt that you get an
advantage from more than 11 stages.
Intelligibility depends (given an acceptable basic vocoder) on what you chose 
to do with sibilants.


paul perry (Frostwave analog fx) Melbourne Australia


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