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  1. Augmented Hurdy Gurdy Experiments

    https://www.youtube.com/watch?v=hPGKeMdRU5I

    As I can’t currently commit to building a new series of gurdies due to my living situation, I’ve been keeping myself busy developing the MIDI system for my instruments, to develop new extended, augmented playing techniques.

    This video is the first demonstration of some hybrid electronic-acoustic experiments using the prototype MIDI system installed on my hurdy gurdy.

    0:22 Technique: Pitch-shifting Polyphony

    Gurdy MIDI and Audio → Apogee ONE → Macbook running a puredata patch

    Monophonic acoustic gurdy signal is pitch-shifted down in real time to play chords and harmonies. Chords and intervals on the keyboard can also be used to pitch-shift the trompette signal (0:55) or the drones. Inspired by an idea from Sébastien Tron.

    1:18 Technique: Expressive MIDI Controller

    Hurdy Gurdy MIDI → DIY Hybrid Poly Synth based off Mutable Instruments Ambika

    The keyboard and wheel sensors send MIDI note, expression and polyphonic aftertouch messages to a polyphonic synthesizer. In this case a split keyboard effect is used to play two sounds.

    1:36 Technique: Layered Acoustic and Electronic Sound

    Hurdy Gurdy Acoustic audio, Gurdy MIDI → DIY Hybrid Poly Synth based off Mutable Instruments Ambika

    1:36 The acoustic string plays a melody, the bottom half of the keyboard controls a synthesizer with a long release for subtle held chords

    2:08 Using trompette technique can send MIDI messages, used here to play synthesized percussion on an Ambika voice assigned to MIDI channel 10, whilst the keyboard plays chords.

    2:30 Acoustic trompette and melody string sound layered over subtle polyphonic synthesized chords

    Playing, Instrument and Software: Barnaby Walters https://gurdy.is https://waterpigs.co.uk
    Polyphonic Pitch-shifting idea: Sébastien Tron
    Filming, editing: Adriana Borger

  2. Some tips for building a Mutable Instruments Ambika, based on my experiences:

    Based on the part numbers in the BOM, suppliers will sometimes pick a CD4050 chip. These are not fast enough and will cause SD card access to fail, it’s necessary to use a 74HC4050.

    If you’re using a 74HC4050 and SD card access is still failing, check whether communication with all of the voicecards works. I had a lot of issues where failing or badly connected voicecards would interfere with the serial lines and prevent SD card access from working.

    On that note: shell out on good quality stacking headers for the voicecards. I picked cheap ones, and suffered a long series of hard-to-debug issues caused by them not reliably connecting. I ended up having to coat all of their legs in solder to make them thick enough to reliably connect. Good headers are worth the premium to avoid these headaches.

    The 3.3V regulator, DACs and all the MCUs can be obtained free from the Microchip samples service if you’re willing to do it over a few months in limited quantities of two part numbers at a time.

    My Pololu USB AVR Programmer wasn’t able to provide enough power whilst programming, so I had to power the boards for programming. For the voicecards, having both 6 pin headers connected interfered with programming because of data being sent to the voicecards over the serial lines. I ended up powering up the motherboard, placing a stackable connector in the power/audio socket voicecard socket and plugging the voicecard into that for flashing, so that it’s powered but the serial lines are disconnected.

    I programmed my Ambika with the YAM firmware to get those smooth sounding PolyBlep square and saw waves. I built the firmware myself, downloading CrossPack 2010-01-15 which provides avr-gcc 4.3.3, the correct version for compiling most old MI AVR firmwares.

    I would recommend buying higher quality pots and encoder with metal shafts rather than the flimsy plastic ones in the BOMs. There are so few on the Ambika that the added expense is only a few euros in total. An Ambika is such a large time and financial investment that there’s really no reason to use flimsy, wobbly plastic pots.

    I got my PCBs from the Pusherman group-buy, they‘re very cheap and work fine.

  3. I built an Ambika to join my family of Walnut Mutables!

    I messed up the LED holes in this one, but the laser engraved front panel graphics and text came out really well. The back panel is acrylic so I can admire my electronics handiwork and Emilie’s amazing design any time.

    I took the opportunity to give my Shruthi a knob upgrade, too.

  4. FREE: ATmega1284p TQFN to DIP adapter boards available for Shruthi/Ambika/open source work!

    TL, dr; I had a batch of adapter boards for the ATmega1284P (a pin-compatible upgrade to the ATmega644 used in the Mutable Instruments Shruthi and Ambika open source synthesizers) built which enable an SMD version of the chip to be inserted into the DIP socket on the MI boards. I now have loads of them and am giving these boards away for free to people who want to work on open source Shruthi/Ambika firmware! I’m also happy to assemble them for a few euros.

    For context:

    Why the ATmega1284P?

    This chip is a drop-in, pin-compatible upgrade to the ATmega644 used in the original Ambika and Shruthi designs, which provides twice the flash available in the 644p. This is particularly important for Ambika firmware development because the stock firmware, and YAM, uses up almost all the space.

    Why not just use a DIP ATmega1284p, if they’re pin-compatible?

    As previously discussed on the Mutable Instruments forums, the DIP ATmega1284p chips have a hardware fault related to the UART used for MIDI functionality which can cause the chip to crash. The SMD version of the chip apparently doesn’t have this fault, and therefore using the SMD chip via an adapter board should fix the problem and act as a drop-in replacement without having to totally redesign the synth.

    I designed this board last month and now have 44 of them. I’m sending some to the developer of the excellent YAM firmware, and will experiment with a few myself, but I have no need for so many.

    So, if anyone’s interested in doing firmware development work on Ambika or Shruthi, or using these for any other open-source purposes email me barnaby@waterpigs.co.uk your address, paypal me the shipping costs if it’s going to be more than a couple of euros, and I’ll send you some boards!

    I’m also happy to assemble the boards with headers and ATmega chip for €8 + P&P per board, if anyone wants.

    Disclaimer: the boards are untested, and I personally have not tested them with the shruthi hardware or firmware! I may not have time to do so but will post my experiences here when I get round to it. Point is, these boards are strictly experimental with no guarantee they actually work!

    Boards in stock as of 2017-11-18: 32