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The Sound of Thunder is the official expander for the Tyme Sefari Mark II. It features a bank of switch and gate controls to enable additional operating modes, as well as additional I/O for stereo operation.

Four new modes are available on this expander, represented by eight toggle switches and gate inputs. To enable each, flip the associated switches up, or insert a 5V gate signal into the input. The new addition of the gate jacks allow full remote control of the Tyme Sefari's recording mode, allowing unique rhythmic effects and controllable corruption of the sampled audio signal.

audio format control

The first two switches control the format of audio that the Tyme Sefari records to its internal memory. Four choices are available, represented by a combination of the two switch settings and explained by a graphical key on the front panel. The four choices are 16-bit linear, 12-bit linear, 12-bit logarithmic, and 8 bit linear. The 16-bit mode is the default under which an unexpanded Tyme Sefari operates. The 12-bit linear is of slightly lower quality. The next two modes double the available recording time due to their decreased consumption of memory. The 12-bit logarithmic mode compresses the signal into a single byte, using a scheme originally designed for 1970s-era digital telephony. The 8-bit mode is the fuzziest of the bunch and the most straightforward, mimicking the behavior of the classic "mark I" Tyme Sefari.

While the subtle differences between each recording format may seem uninteresting, they are made musically useful by making the Tyme Sefari unit ignorant of the format of the data stored in its memory. It will decode audio according to the format switch settings, leading to interesting and often extreme distortions when the playback format does not match the original recording. Since the transport speed also changes with some of the format settings, one may achieve speed doubling or halving as well.

pitch shift mode

This switch enables a crude pitch shift effect. It directs the playback head to run at a different speed than the record head, controllable by the large frequency knob and CV input. This will occasionally cause glitch effects as new data being recorded overruns the playback of old audio. By turning up the feedback, one may achieve bizarre, frequency-staircase "crystallizer" effects, causing the pitch of the delayed audio signal to endlessly travel in one direction. The pitch shift control changes the playback speed of the audio to one octave above or below that of the original recording, with the distortions present in the sampling rate mismatch contributing to the unique character of this effect.

stereo mode

Flipping this switch will enable the audio input, output, and attenuator at the bottom of the Sound of Thunder panel. Tyme Sefari will now record and play back in stereo. Since this mode consumes twice as much memory and runs the transport twice as fast, it can also be used to temporarily speed up the sound of a mono recording. In stereo mode, the feedback loop of the Tyme Sefari acts as a summed mono signal.

circuit bending

This group of four switches will skew the internal data and address busses of the Tyme Sefari in unpredictable ways. Dependent on the sampling rate, input audio characteristics, and loop settings, the module will crackle, fizz, escape into out-of-bounds memory locations, and irreversibly foul the audio playback. Periodically triggering these four switches with external gates, with live recording and feedback is a sure way to access a world of sounds previously available only to those brave enough to modify old digital keyboards with experimental circuit bends.


Quickstart manual (pdf format)


  • 8HP Width
  • 5 mA +12V
  • 0 mA -12V
  • 0 mA 5V
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