Ensemble Circuit Configuration Questions

[Sean Costello]

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