Ensemble Circuit Configuration Questions

[Harry Bissell]

I've built a phase shifter (6 stage fet tuning, the usual..) with the
outputs A+B and A-B
(A = input B= output of phase stages) It gives a very subtle effect when in
the air in stereo (or a very wired effect in headphones)  Did the same with
a reverb (a'la National Semi Audio databook, which inspired me to make the
phaser). Kind of more simple than you were thinking, I'll bet... but someone
might like the idea ....
:^) Harry

Sean Costello wrote:

> Hi all:
>
> I am doing some research into the "ensemble" effect used in the string
> ensembles of the 1970's. So far, most of the ones I have seen use 3
> short bucket-brigade delay line chips in parallel, with the outputs
> mixed together. Although the Eminent patent describes mixing the
> original signal with the output, the string ensemble circuits I have
> seen only mix together the delayed signals. As far as driving the delay
> lines, I have seen 2 different configurations:
>
> 1) Each delay line has a seperate LFO, running at a different speed. As
> far as I know, the ARP Omni is the only synth that used this technique.
>
> 2) Two LFO's are used for the 3 delay lines; one runs at 6.5 Hz or so,
> while the other one runs at .75 Hz or so.
> -Each LFO goes through a phase shifting network with 3 outputs, each of
> which is shifted 120 degrees (i.e. one at 0 degrees, one at 120 degrees,
> one at 240 degrees). -Each delay line is modulated by a sum of the
> identically phase shifted outputs of the 2 LFO's, i.e. Delay line 1 is
> modulated by the 0 degree output of the .75 Hz LFO and the 0 degree
> output of the 6.5 Hz LFO, delay line 2 is modulated by the summed 120
> degree signals of the 2 LFO's, delay line 3 is modulated by the summed
> 240 degree LFO signals.
> This technique was used by the Solina/ARP String Ensemble, the Eminent
> organ, the Moog Opus 3, and probably others.
>
> Do people know of other techniques used for generating ensemble sounds?
> What about the Roland ensemble/Dimension choruses - anyone know how
> these worked? I have seen a Roland Vocoder ensemble circuit that used at
> least 4 BBD chips, in a strange serial/parallel configuration - does
> anyone know the theory behind what is going on in there? Do people have
> preferences for different techniques?
>
> Also, has anyone tried creating ensemble sounds using techniques besides
> time delay? Would several parallel allpass circuits generate such a
> sound? I've tried this in Csound, with little success, but perhaps
> others have generated nice sounds in this manner.
>
> I would love any details people might have. I am working on a Csound
> orchestra to implement the Solina/Eminent technique - I already have a
> "choir" orchestra that uses the ARP Omni technique in combination with
> resonant bandpass filters for the formants. Any details of the internals
> of other ensemble circuits would be greatly appreciated - I will be
> putting up a web page describing my choir orchestra, and could put up
> another page describing various ensemble circuits, with sound files of
> how they are implemented in Csound.
>
> Thanks,
>
> Sean Costello