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

> Fax +49(89)45841-111 |Franziskanerstr. 38, D-81669

München

> email: florian.anwander@c... | http://www.consol.de