Overview
The Shruthi-1 Synthesizer was originally manufactured by Mutable Instruments and is a hybrid digital/analogue monosynth. It was available from Mutable Instruments to customers in kit form for self assembly. This versatile synthesizer has the convenience of two digital oscillators and a sub oscillator, supplied via the 8-bit microcontroller. Classic analogue waveforms can be accessed as well as wavetable synthesis. Digital algorithms can be employed for bit crushing, phase distortion and XOR modulation. The mention of 8 bit may put some potential purchasers off, but many classic synthesizers have 8 bit digital oscillators.
The analogue part of the synthesizer is the filter. On launch, the Shruthi-1 featured an SMR-4 analogue filter. This 4 pole low pass filter sounds sounds very warm and not too dissimilar to filters used in some very sought-after classic Roland synths. The filter is not limited to only creating sound in the circuitry within the device, the filter can also be fed via the audio input allowing external sounds to be processed. The filter was later revised to an SMR-4 MkII version, retaining the sound, but reducing the part count.
A hybrid digital/analogue approach allows the synth to sound like a typical classic subtractive synthesizer but it can also be used to create digital sounds similar to those generated in 8 bit computers and consoles.
Firmware
The firmware in the instrument is issued under the GNU General Public License. This allows the end user the legal freedom to modify the firmware. The C++ source code is available on github for download.
Control
The Shruthi-1 only has five rotary encoders and four buttons on the front panel, yet programming the instrument is very intuitive due to the way the menu system is implemented. It is a very controllable device and includes a twelve slot modulation matrix. MIDI support is good and a large number of parameters are accessible for real time automation. An arpeggiator is built-in. Although it is effectively a monosynth, it can be chained together with other Shruthi's to add extra polyphony.
Filters
On launch, the Shruthi-1 featured an SMR4 filter. Mutable Instruments also released other filters for use with the main control board:
- 4 Pole Mission - based on the SSM2164 chip
- Dual SVF - combines two multimode filters
- Polivoks - clone of the filter used in the Russian Polivoks synth
- LP2 + Delay - filter inspired by the MS20 LPF with a digital delay
- FX/Digital - lo-fi digital filter (not analogue)
A comparison of filters can be heard on Soundcloud.
Other filters have been added by third-parties, including:
- To-LAD-4tr - transistor ladder design influenced by Moog products
- Shruthacon - reinvention of the Steiner Parker filter
- CEM3379 - using a Curtis CEM3379 chip