Shruthi FAQ

I want one, but fully built. Will you sell me one please?

All the decisions that have been taken during the design of this product (feature set, choice of processor, board design, part selection) were motivated by one goal: make it a synth that you can build and service yourself – eventually from scratch, with standard self-sourced parts. Because of these choices, the assembly of our products cannot be efficiently automated, and hand-assembly is the only way to go. Mutable Instruments cannot offer this service in a cost-effective way.

However, you might find someone willing to build one for you. You can browse a list of experienced builders willing to offer their services on the Mutable Instruments forums.

What is the difference between Anushri and Shruthi? Which one do I need?

The Shruthi uses digital oscillators and a digital modulation matrix; and the functions assigned to its four knobs are context-dependent. As a result, it can pack an amazing amount of synthesis capabilities in a small size and low part count, covering various synthesis types and offering extensive modulation options.

Anushri was designed with three very different goals in mind: keep the signal chain analog, use separate controls for all important synthesis parameters, and make it fun to use as an inspirational “groovebox”. Given these constraints, we had to get back to basics – it would have been impossible to pack the 2 LFOs, 2 envelopes, 2 oscillators and multiple synthesis techniques that the Shruthi-1 delivers in an all-analog board! As a result, Anushri’s sound palette is more limited; but what it does – leads, basses, and analog FX – it does it well and with character! There are areas indeed in which it actually beats the Shruthi-1 hands down: PWM, FM and hardsync sounds – not the easiest ones to emulate with digital oscillators!

Anushri’s sequencer is very direct: press rec, input notes step by step, press rec again when you are done, then press play to start. The Shruthi-1 sequencer has more options – in particular control values can be recorded at each step – but is not as immediate. Finally, Anushri’s secret weapon is the built-in drum section – rough in sound and unusual in interface, but very inspiring!

So if you want to know what it’s like to modulate the balance between two wavetable oscillators with a step sequencer, while sweeping filter resonance with a 25 Hz LFO, the Shruthi-1 is the right synth for you – a sound design beast. If you are looking for solid bass/leads analog sounds, record a 4 bars loop, fire up a kick drum and immediately start a microparty in your studio, Anushri is the better choice.

I have never soldered anything but am willing to learn, is this kit difficult to assemble?

The Shruthi is not difficult to assemble. The assembly instructions are very detailed, part values are printed on the PCB, and there are no surface mount parts. However there are more than 200 parts to solder, increasing the risks of doing something wrong if you are not 100% sure of your soldering skills. While there is an increasing group of people having successfully built the Shruthi without prior experience, there are also a few occurrences of people having damaged their kit beyond repair.

Our advice? If you have never soldered anything in your life, go grab a small kit at your local electronic store, assemble it, and come back to the Shruthi afterwards. Here are some recommendations of simple projects gathered from other beginners. Something as simple as buying veroboard/stripboard, a bag of cheap resistors, and doing 100 soldering joints will give you some experience and boost your confidence.

Also, while assembly is easy, troubleshooting an assembly mistake can be difficult and might require more skills (using a multimeter, following a schematics, desoldering parts). If you are a beginner, make sure that there is someone around you willing to help in case things do not go as expected, and don’t be scared at the thought of talking about your mistakes on the forum.

4 knobs, seriously? What’s the point of making a complex synth if you make it that hard to edit!

User interface is a very subjective matter, but all the Shruthi users agree that it is a very intuitive and easy to program synth, and that the pages / parameters layout can be learnt very quickly (that is the reason why we don’t label the 6 switches – the same way note names are not written on piano keys). But if you insist, yes, it’s possible to build a “1 knob per function” programmer for the Shruthi!

This “unofficial” project has been developed by forum member fcd72. Join the forums, look around if there’s an ongoing batch in preparation, and do not hesitate to ask!

8-bits? Does it mean it sounds like a gameboy?

8-bits has been used a lot recently to refer to the aesthetics associated with early 80s gaming consoles and home computers. Those computers used dedicated sound chips (such as the AY-3-8910, MOS 6581 or C012294) featuring high-frequency (clocked at several MHz) digital oscillators, and in the case of the SID, an integrated analog filter.

8-bits also refers to the resolution (fairly low by modern standards) of a digital circuit storing or processing audio signals. Early 80s wavetable synths and samplers (CMI Fairlight, E-mu Emulator , PPG Wave, Ensoniq ESQ-1, Kawai K3) all used 8-bits sound generators.

The Shruthi is closer to the latter than the former.

Is this thing Arduino powered?

Mutable Instruments’ DIY products use the Atmel ATMega line of microcontrollers, which are also used in the Arduino development boards.

However:

  • Our projects are clocked at 20 MHz, to get the best (and still modest…) performance out of the chip. The Arduino boards run at 16 MHz, and as such, a lot of code coming from Arduino-land will not run on Mutable Instruments hardware without changes.
  • Our projects are designed for firmware upload through a standard AVR ISP programmer, or through MIDI, not with a USB>serial interface.
  • Our projects do not make use of any library, programming style, or development tools coming from the Arduino project.
  • Our projects are stand-alone systems – they do not require Arduino boards as their “brains”.

What is the origin of the name?

Our first project, the Shruti-1 originally was an all-in-one tampura/shruti box/lehera machine generating sound with Casio-CZ style phase distortion, but after adding some menus to tweak the sound parameters it quickly morphed into a synth. The “ShruTHi” spelling was coined during discussions with Tim Parkhurst about the use of the TH-201 (aka “Mankato”) VCF design in the Shruti-1. At this point, the decision to redesign the product with an “open-ended” analogue section was taken. Shruti means “what is heard” in Sanskrit and refers to the pitch class in the context of indian music. Shruti is also a common (girl) first name. Like many common indian names, Shruti is often transliterated with an aspirated consonant in South India, so Shruthi is commonly seen as a name too.

Fans of chiptunes and south indian cinema will chuckle at the thought that actress Shruthi once dated Sid.

No USB? 20 MHz 8-bit chip? No DAC? No assembly? Do you know what you’re doing?

Yes, some of the technical choices taken at Mutable Instruments are not particularly cutting edge, or are very unusual compared to standard industry practices.

The reason is that there’s a part of education in Mutable Instruments’ mission; and our DIY products are designed to show you as much as possible what’s going on under the hood, and to maximize the opportunities to get you involved in tweaking things. For these reasons:

  • Only through-hole parts are used – no tiny LQFP surface mount packages!
  • We stay away from MCUs which do not have free/open-source development tools, or which require proprietary IDEs. If it’s not dead easy to get a standard gnu toolchain + programming tool for a chip, we just do not consider it. “Be the change you want to see in the world” etc.
  • We use assembly language only for a small number of signal processing primitives, the rest is written in more readable C++ to make it easier for you to dive into the codebase. Yes, C++, our projects are complex and there are things in C++ that help us structure them better.

A consequence of the first two points is that we are limited in our choices of MCU to the Atmel ATMega series (OK, we’re going to give a chance to these new NXP Cortex-M0 parts!) – which do not features a USB interface – and that we sometimes cut corners in accuracy/signal fidelity to get the most out of these little chips. A consequence of the third point is that there are still a few % of CPU power untapped in our projects, that could be regained by instruction micro-management.

How can I get a kit with the special filter boards?

The only available kit includes the SMR4 mkII filter board. The SMR4 mkII filter is an easy build, with step by step assembly instructions, and it is very likely that any mistake you’ll do while building this filter has been done by someone else in the past, making troubleshooting easy.

The other filter boards are more advanced projects (without step by step assembly instructions), and we do not recommend beginners to start with them. We do not offer these filters as kits, because if you have the required experience to build them, you should also be comfortable with buying your own parts – and probably already have your own stash of TL072 and 100k resistors at home!

Does the Shruthi have CV/Gate inputs/outputs?

The Shruthi has 2 spare analog signal output ports; and 4 spare analog signal input ports – labelled “CV” on the board.

A few things worth knowing about these:

  • The input CV must be constrained in the 0V .. 5V range. Voltages outside of this range will damage the MCU. This is not a problem when wiring a pot, joystick, sensor, LDR, etc, but it could be a problem when adding jacks for connecting external signals from a modular. We recommend adding a protection circuit on the inputs – such as two unity gain inverters, the second realized with a single-supply rail-to-rail op-amp.
  • The CV inputs are scanned at a fairly low rate (close to 50 Hz), and their resolution is 8-bit. This prevents audio-rate modulations, and accurate pitch control.
  • The 2 output ports are PWM signals with a 40kHz carrier. Some modules might perform in unexpected ways when receiving such signals. We recommend adding a low-pass filter and optional CV-scaling circuit.
  • The CV outputs are refreshed at 1kHz and their resolution is 8-bit. They are thus not suitable for accurate pitch control.

Is there any kind of warranty or repair service for kits?

We accept returns of goods in the same state as we shipped them (unopened bags of parts). We ship at no cost any part that could be missing or damaged from your kit. In the event you have damaged a part while assembling your kit, we can sell you a replacement.

However, it is your responsibility to ultimately get your kit to work.

In the event of an assembly error, we do not exchange or repair boards. We provide support through the Mutable Instruments forum. Very experienced DIYers are hanging out there and will be happy to join us to assist you.

If your question has not been answered here, you can:

Olivier Gillet, Mutable instruments SARL 2011-2013. Except where otherwise noted, content on this site is licensed under a cc-by-sa 3.0 license.