About Doepfer on vocoders

[Haible Juergen]

> Please read what Dieter Doepfer has to say about vocoders at my
> "vocoder info page" at: http://www.algonet.se/~zzynt
> and have a good moment of thinking about your d-i-y vocoder design.

I found one thing in your Doepfer quote which I'd like to comment:

> All high priced vocoders imply such a treble boost but the
> customers is not aware of this detail as there is no remark in the
user > manuals [Doepfer]

I can only comment on the Sennheiser here (which sure fits into
the high-priced category). 

The Sennheiser does have a clever preemphasis / deemphasis
system for improoved SNR. There is a "treble boost" circuit
in one of its inputs, but this "boost" is then *corrected* by the
individual
summing resistors of each channel output! The idea is the same as
on FM radio, Vinyl records etc, just to keep the noise down. It is
tricky to find in the Sennheiser circuit, because there is only one
filter (the preemphasis), and the complementary "filter" function
is made by the resistor weighting. 

This all has nothing to do with an overall treble boost. Such an
overall treble boost may be pleasant or unpleasant, depending
on the application. But that's what the Sennheiser had its channel
volume potentiometers for: You can shape the overall frequency
response just as you need it. With all knobs at the same position,
you expect a "flat" (well, what "flat" can mean on a filterbank ...)
overall response.

JH.