Wiardgroup

Hi Grant, thanks for this. Very helpful and interesting. I think I did read about the Subotnik technique, maybe in the notes from one of releases.

I came from about the same era as you, I had a simpler system, Roland SH2, CSQ100 sequencer and Dr Rythmn, but I did try and interface everything with everything else. Plus I had a ReVox so I tried and failed to do some click track stuff but the results were better than if it had worked. I still have all that gear. I'm doing a minor repair on the DR-55 and hope to be using that and the CSQ100 for "something".  I need to get the ReVox fixed too. The tape echo is just wonderful. 

ok, I will get back to my Wiarding. I hope to put up some further samples shortly.


warm regards, Mark




________________________________
From: Grant Richter <grichter@asapnet.net>
To: wiardgroup@yahoogroups.com
Sent: Saturday, 27 December, 2008 3:39:44 AM
Subject: [wiardgroup] Mini-lecture on VCO "Attack-Release" generator and "Player Piano" technique


Hello Mark,

> A quick couple of questions, for which there is no rush for an answer....I saw in the hints 
a tips Grant mentioned that a 5V gate on the Classic VCO and WC won't fully open the 
VCA on those units. 
> 
> 1. I have a Kenton convertor that gives 5V or 15V (no 10V). Is 15V safe for the 
oscillators gate?

The "Attack-Release" generator on the Classic VCO and Waveform City is a hybrid of an 
envelope follower and an envelope generator. If a gate is just a step function, 0 to 10 volts 
and back to 0 again. Then by slew rate processing that signal, it will naturally make an 
attack release envelope.

To make an envelope follower, you need something to remove the negative portions of the 
analog audio, otherwise that average of the + and - is zero.

The Gate input has a current limiting resistor and a 10 volt zener diode at the input. When 
processing a normal 10 volte gate, the device is not even activated.

When processing audio, it removes the negative portions of the audio signal, in what is 
called "have wave" rectification. Not an ideal envelope follower, but a usable one essentially 
for free.

In you case of a 15 volt gate signal, it will "chop off" (limit) the signal to 10 volts, and the 
output envelope will be 10 volts, just what you want. There should be no problem using 
the 15 volt gate signal, it will be converted safely to a 10 volt envelope.

> 
> 2. Presumably the Envelators (with the envelope generated into ZMOD of the Mixolator)
 are fine with just 5V?

The ARP 2600 was such a well thought out synth that I actually divide synth history to 
before and after the 2600. It is not completely perfect, but it was the first one to get 
almost everything right. Two well know problems are 

1. DC offsets on the audio which causes "thumping" with the filter and VCA

2. The envelope trigger voltages (once you modded the unit to get at them) had six volt 
thresholds. So you could not take your shiny new 808 or 909 or 606 and run the 
envelopes from the rhythm box external triggers. There were work arounds but it was 
clumsy and a repeated pain. And you really did want to link your rhythm box and 
sequenced synthesizer together, oh yes you did. Just trust me on that.

So in the design of the Wiard modules, trigger threshold were set to work with TTL (5 volt) 
technology like the rhythm boxes from the 80's, and other modern stuff that uses 5 volts. 
The thresholds are nominally set to TTL "High" which is around 2.5 volts.

So a 5 volt gate or trigger will work fine with the Envelators. All the Sequantizer inputs 
also have this 2.5 volt threshold, Step, Reset, Glide, Octave + and Octave - should work 
just fine with patched out 606's and other rhythm boxes.

They will also accept clock, gate and trigger sources from Serge modules in general and 
the TKB in specific.

But that is only the beginning of the story. Here is the deep stuff.

Morton Subotnick worked out an advanced synthesizer technique on the Buchla he call the 
"player piano" technique. Normally a tape recorder can not store the very low frequencies 
that are the control signals humans generate as control signals when we "play" a 
synthesizer.

Subotnick brilliantly came up with a work around using AM (amplitude modulation). All 
that requires is simply controlling the amplitude (volume) of a simple "carrier" wave and 
the very slow signals are stored as variations in the volume of the carrier, and can be 
recorded on magnetic tape.

Upon playback a simple "decoder" recovers the control signals from the amplitude 
variation of the tone recorded on the tape.

To "encode" the signals you need a sine wave carrier from a VCO followed by a Voltage 
Controlled Amplifier (VCA) then going to the tape recorder. The control signal to be 
recorded is used to control amplitude (volume) of the carrier (VCO sine wave) as it is 
recorded to tape.

In the Classic VCO, to record a control signal with a 0 to 10 volt range, patch the SINE 
output to the VCA1 input, set the "VOL" knob to zero, patch the VCA OUT to the tape 
recorder input, patch the control signal to be stored to the VCA ENV jack. 

To record control signals that have negative voltage portion, just advance the VOL knob 
until the most negative excursion, just shuts the VCA off.

Most any VCO frequency (pitch) will work, but since we only have "half wave" envelope 
following, a higher frequency like 1 kHz will give the best results in terms of the "ripple" or 
error signal generated by the "decoder" during playback.

As you have probably guessed, the "decoder" for an AM encoding technique is an envelope 
follower. The "Attack" and "Release" controls are used to modify the control signal after 
recording. Normally, another unit called a "Gate Extractor" is needed to interface the 
incoming envelope follower signal to trigger onboard envelope generators.

The low threshold voltage on the Envelators and "forgiving" design of the Envelator GATE 
input, allow direct connection of the AR ENV output to the GATE inputs with only some 
tweaking of the Release control needed to get a repeatable envelope trigger. A "Gate 
Extractor" is optional for use of the AM encoding technique on the Wiard instrument.

I hope this explanation will help to clarify why the "AR" generator on the VCO modules 
does not precisely follow the trigger thresholds and behavior of the Envelator and 
Sequantizer modules. Some compromise was needed to allow the Classic VCO to be used 
as a self contained "channel" for the play piano control voltage storage technique.

The ability to record and store long complex controls signals, which can then be brought 
back into the instrument and used like "live" playing signals is extremely powerful. It 
allows you to use all the modules to generate the complex control shapes, and then the 
same modules can be repatched for use at audio frequencies, this doubles the 
effectiveness of the the instrument. It also allows the player to have both hand free for 
"knob twizzling" and other techniques which add dynamics and expressiveness during 
playback. Essentially the ability to "conduct" the stored performance.

Thanks for reading and have a Happy Holidays

Grant Richter