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Triadex Muse in Javascript

Donald Tillman, Sept 3, 2017

This is a software simulation of the Triadex Muse that runs in a browser.

The Muse was a digital algorithmic music composer invented in 1969 by Marvin Minsky and Edward Fredkin at MIT. It was built from elements of computer digital logic circuitry; gates, registers, counters, etc. While strongly associated with electronic music, it was not a "synthesizer" as it only played a fixed level square wave.

muse photo

Minsky and Fredkin formed Triadex to manufacture the units, which sold for $300.00. Accessories included an amplifier and a light show in matching enclosures. Multiple Muses could be linked together and synchronized.

The Muse is incredibly rare; one report claims that only 280 were built, and a small fraction of those are likely in working condition today. And that's a shame, because this was a remarkable device and we can learn much from it.

muse trio

Directions:

There are eight 40-position vertical slide switches that control the composition process. Details on those are below.

The OFF-RUN-START switch turns the unit on and can reset the state to the beginning.

The STEP-HOLD-AUTO switch single steps, halts, or runs the sequence.

The REST switch turns the lowest note into a rest.

How It Works

The 40 rows are the available binary (0,1) sources. These are:

OFF and ON
Steady 0 and 1 values
C 1/2
The clock pulse, a sqaure wave that triggers the rest on the high-to-low transistion
C1, C2, C4, C8
A 4-bit binary counter incremented by the clock pulse
C3, C6
A 2-bit binary counter incremented every 3 clock pulses
B1 through B31
A 31-bit shift register clocked by the clock pulse

The four INTERVAL switches select from the binary sources to set the pitch. INTERVAL A-B-C, are binary weighted 1, 2, and 4, respectively, and map into a major scale. INTERVAL D raises the pitch an octave.

The four THEME switches select from the binary sources to set the value for the top of the shift register through an XNOR function; 1 for an even number of one's, 0 for odd.

The counters provide repeating patterns. The 4-bit counter repeats every 16 counts. As the clock pulse is a square wave, you can double the count to 32 by including the clock pulse itself (which explains the funny name on the label). Or you can triple it to 48 by including the 2-bit counter and get some 3-against-4 patterns in there. Or both for a 96-note pattern.

The shift register can provide delayed versions of any combination of those signals. Or it can recycle a pattern by feeding back a single B output.

But the really interesting compositions happen when two or more shift register signals are fed back with the THEME switches. We call this a Linear Feedback Shift Register (LFSR) and it has many very interesting properties; books have been written about it.

Compositions

Here are some "compositions" transcribed from the User Manual. Click on one to load it into the Muse.

Name Intervals A,B,C,DThemes W,X,Y,ZRest

More on the Muse

The Muse was designed with 1969 technology, and it's easy to forget how severely limited the available selection of chips was back then. But new functions were also being introduced at a rapid rate.

From the photos on the MuffWiggler thread (below) there are 29 chips, probably TTL logic. There are 7 chips in a line, probably 7406's, that drive the lamps (not LEDs). The counters might be be 7474 D-flops. The shift register appears to be implemented with 3 large 24-pin packages providing 10 bits each.

It's a pretty complex machine for a 1970 consumer product.

There is some contention on how the audio oscillator works. Hal Chamberlin claims it's a VCO, but the board doesn't appear to have an analog oscillator on it. The patent claims it's a 1 bit serial accumulator (!!!) built with a shift register recirculating the value around a single bit full adder. That would be crazy but weirdly practical if a 16-bit accumualator was expensive to implement with the available chips at the time. The Programming Manual claims it's a divide-by-N counter, which I think is most likely.

After the oscillator, a flip-flop generates a note an octave below, and the INTERVAL D value switches between the two. Note that a major scale has 7 notes, while a 3-bit binary quantity has 8 values, so there is one note of overlap.

Musicality

There is a subtle genius in the design of the Muse: Songs and other musical pieces often include scales, riffs, patterns, call and response, and thematic development. And sure enough, all of those elements are available here. (!!!)

The Muse uses two differnet counters and an LFSR, and that was totally intentional.

LFSRs can generate sequences with mathematically random distribution; they're the go-to source for random number generators. And with 31 bits, the sequence can be up to 231-1, or 2,147,483,647 steps before repeating. So we shouldn't expect a melody from a lengthy LFSR.

A single counter with a binary weighting plays a scale. A single counter with a non-standard weighting provides a riff, a repeating figure. Use both counters for a sequence with repeating intervals from different starting points; that's a pattern.

You can use the shift register without feedback to delay a counter output for call and response, or another style of pattern. Use the shift register with two or more feedback inputs and it's an LFSR random number generator. And you can greatly diminish length of the sequence by positioning the taps.

Use multiple taps off the LFSR for other interesting patterns. Combine the counters with the LFSR, and you've got thematic variation. You can tweak the balance between the predictable and unpredictable, with patterns within patterns.

It's not easy or anything, but the mechanims are present.

This Implementation

This is implemented in HTML5 and Javascript, about 6 pages worth of code. And much easier than finding a source of 40-position slide switches.

I've tried to make this as true to the original as possible, even though I have never actually seen a Triadex Muse. I based this on the Triadex manuals, the patent, and scrutinizing some terrible videos in slow motion. (I would sure like to see a demo video by someone who actually knows something about the machine... and owns a tripod.) I have no idea how the Muse light show unit works, so I just winged it here.

The description in the Muse section in Hal Chamberlin's, Musical Applications of Microprocessors is very helpful on the whole, but be aware that pretty much every detail is inconsistent with the other sources.

There are subtle bugs. The STEP switch should raise the clock high when pressed, and low when released, while it currently just alternates the clock. The tempo is based on the Javascript system timer, and it can slow down when you switch to another window. I might address these later.

A future improvement might be the ability bring up multiple instances of the Muse and synchronize them.

References

Triadex Muse User Manual, Triadex Inc., 1970

Triadex Muse Programming Manual, Triadex Inc., 1970

US Patent 3610801, Digital music synthesizer, Filed Feb 16, 1970, Granted Oct 5 1971.

Hal Chamberlin, Musical Applications of Microprocessors. 1980. Long out of print, but you can find a pdf version if you look.

MuffWiggler thread, Triadex "The Muse" pics and sound clips, 2010. Interesting photograph of the internal construction.

Photos grabbed from 120 Years of Electronic Music and Matrixsynth.

Copyright 2017 J. Donald Tillman
email: don@till.com
web page: http://www.till.com