Doepfer

hello florian,

as usual, your explanation is just great
and very much apprechiated, thanks :-)

best wishes

ingo



--- In Doepfer_a100@yahoogroups.com, Florian Anwander 
<Florian.Anwander@c...> wrote:
> Hi!
> 
> There were several postings regarding module suggestions, which 
show 
> basically all for the same thing: a voltage controlled audio delay.
> 
> I experiment a lot with VC delays and similar techniques and would 
like 
> to share my experience (I write this while a boring conf call, I 
hope I 
> don't mix something up...):
> 
> We have to differ to kinds of fields of application:
> 1.)Delay in the sense of "echo".
>    The delaytimes begin with ca. 10ms and may end somewhere
>    above 100ms and or more than a second. The modulatable range has
>    not to be very wide: 75% to 150% of the base delaytime are
>    usually enough. This is already the maximum, the most delays
>    provide!
> 
> 2.)Delays for Chorus and Flangers.
>    The minimum delay time should be quite short (0.1ms). The maximum
>    must not be longer than 50 ms. The modulatable range is enough
>    with 75% to 150%
> 
> 3.)Delay for Resonance-based synthesises like Karplus-Strong.
>    The minimum delay time has to be very (!) short (0.01ms).
>    The modulatable range (especially for tonal synthesis
>    applications) has to be much(!) wider:
>    10% to 1000% of the base delaytime would be great.
>    25% to 400% are a must to have a useful tonal range of four 
octaves.
> 
> Also we have three different techniques to build an audio delay:
> 
> A.) BBDs (Bucket Bridge Devices).
> The delay time is direct depending from the Clockrate. Very high 
clock 
> rates are technically not really feasible to my knowledge (this may 
be 
> wrong -> Dieter?). Low clock rates sound awful, not only because 
the 
> clockrate comes to the audiorange, but also because the hold time 
of the 
> single "buckets" is reached, and the signal is distorted heavily.
> So to get a delay for Karplus-Strong stuff we would have to use 
only a 
> short Bucket bridged row. This would urge us to use low clockrates 
for 
> the longer delay times, which cannot be recommended. So BBDs are 
not 
> useful for Karplus Strong.
> For Delay in the sense of Echo, BBDs have a too bad noise to signal 
> ration. Delays above 250 msec become worse and worse.
> BBDs are nice and smooth sounding for Chorus and Flangers
> 
> B.) Digital memory based delay, A/D-converter has a constant clock:
> This is the type most modern delays work like. The A/D works with a 
> constant clock. The change of the delay time is achieved mainly by 
> changing the size of the memory, which is used. If this change is 
done 
> while working with an audio signal, the audio signal will have 
spikes, 
> like a "jumping" CD. The old Roland delays simply muted the signal 
when 
> changing the delaytime. Very modern dsp-based delays can cover this 
by 
> smoothing algorithms, which are difficult to develop.
> Small delay time changes can be achieved by modulating the reading 
clock.
> This kind of Delays is good for "echo"-like delays and for 
> chorus/flange. It is unusable for karplus-strong stuff.
> 
> C.) digital memory based delay, one clock for ecerything (A/D, 
memory 
> reading, and  D/A).
> This is a quite old fashioned digital delay type. The memory size 
is 
> constant. All changes of delay times are achieved by changing the 
> clockrate.
> The clock may come from a simple highspeed VCO (not a PLL-based 
one, but 
> a CEM3340 with small C-value).
> The main disadvantage against the type B is, that the signal 
quality 
> gets worse the lower the clock frequency is.
> The main advantage is, that the delay time can be changed in a 
quite 
> wide range. Also the change can be done in realtime without 
producing 
> spikes or similar unwanted side effects.
> This is what is required for Karplus-Strong synthesis (or similar). 
Also 
>   Chorus and Flanger are ok with this. "Echo" like delays ar not 
that 
> goood, because of the bad quality of longer delays (lower 
clockrates...).
> 
> 
> So I am not sure, whether Doepfer simply can build one "delay"-
module 
> for everything we usually subsume under "delay-effects".
> 
> 
> Regards, Florian
> 
> 
> 
> -- 
> Florian Anwander                  |ConSol
> Tel.   +49(89)45841-133           |Consulting&Solutions Software 
GmbH
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> email: florian.anwander@c... |http://www.consol.de