Tag: eurorack

  • Glitch Delay – more progress

    I’ve been working pretty hard on my glitch delay module the last few months. As you may remember it’s sort of a cross between my previous AudioFreeze project and a digital delay. It consists of a delay line with a write head and a read head. The difference being the read head is basically looping a tiny buffer behind the write head. This is implemented using 2 read heads which crossfade between each other to avoid popping. It has 2 modes now. The loop window either moves through the buffer, or statically jitters, at a rate controlled by a pot.

    My original experiments were with a Teensy 3.2, but its rather limiting 64k of memory meant I only had about half a second of audio buffer. I’ve now moved to using the Teensy 3.6, which has a whopping 256k of ram! I’ve also implemented 12-bit audio (2 samples stored in 3 bytes), which gives me an audio buffer of around 3 seconds, which is enough to get nice repeating loop effects. I’m using the PCB board I designed for my AudioFreeze project which was designed for Teensy 3.2. The 3.6 is twice the length, but by crafting a tower block of female header I was able to raise the Teensy over the height of the ribbon power connector.

     

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    Initially I had a very peculiar issue where the module would only work when powered by USB, not when in the modular case. Weirdly, when I was putting the multimeter on it, to test power was getting to the board (which it was), it would sometimes startup, and then work fine. It turned out the case wasn’t supplying enough current. The Doepfer power board only supplys 50mA on the 5V rail, and 100mA on the 12V rail. I tried making a small add-on board with a voltage regulator on, so I could you the 12V power, but it still wasn’t enough. I ended up adding a separate power board, and powering it with a 5V wall adapter directly.

     

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    With all the extra processing power the 3.6 provides I was able to create 3 separate play heads, all looping audio at different pitches which is mixed together. One plays at 1/2 speed (1 octave down), one at normal speed, and one at double speed (1 octave up). Currently the mix ratios of these are fixed as I’ve run out of knobs on my board!

    Here’s a very simple demo, you can hear the acoustic sound of the guitar in this video, normally I’d want the effect to be totally wet, but it does serve to show you what the original audio is doing..

     

     

    This diagram shows how the processing blocks are organised. It’s the glitch delay block that’s really doing all the work.

     

    I actually played with this live at my last gig at Spirit of Gravity. I hope to incorporate it into my material more when I’ve properly learnt to play it! Next up, I may try to add CV control to all the parameters. I’d also like to move away from using the audio shield, as I’m not really taking advantage of the 16-bit DACs/ADCs. I’m really only using it so I can use the Teensy ADC to read the pots. I’m planning on designing a new PCB and using a PIC chip to handle all of the pots and CV interface stuff and then connect that to the Teensy via I2C, but I’ve no experience of that, so that’s a whole new adventure!

     

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    As always, code is here

  • Work in progress Glitch Delay

    So I’ve been beavering away on a new Eurorack effect based on the Teensy board again!

    Added a very rough demo, which starts with a dry loop, then entirely wet glitch effect. Dials from top to bottom are

    1. Glitch window size
    2. Glitch window speed
    3. Feedback
    4. Dry/Wet mix

     

     

    The effect is sort of a cross between my previous AudioFreeze project and a digital delay. Is consists of a delay line with a write head and a read head. The difference being the read head is basically looping a tiny buffer behind the write head. This is implemented using 2 read heads which crossfade between each other to avoid popping. The window (the size of which is controlled by pot 1) moves (forwards only currently due to lack of buffer size) through the buffer at a speed controlled by pot 2. There’s a certain element of randomness added too each time the loop restarts. It then has to jump over the write head as it cycles through the buffer.

    Next stage is to extend the buffer time by adding more memory chips to my Teensy based board. I should hopefully be able to extend the time time from ~0.5s to around ~7s. This should give a lot more time to hear glitches repeat before the write head loops back around and the play heads have to skip over it.

    https://github.com/cutlasses/GlitchDelay

     

  • Build your own AudioFreeze

    I’ve added the Gerber files to GitHub so anyone can build the module if they like. As a disclaimer this module should be seen as a prototype. IT HAS NO POWER FILTERING OR SHORT CIRCUIT PREVENTION, if you plug the ribbon cable in the wrong way you may damage the board and potentially your other modules. Also your case must supply 5V power (some don’t). As this was my first PCB I wanted to make it as simple as possible. I’m merely making it available as a resource for people who want to make their own boards. If you do build your own I’d love to see it. Please tweet me @scolar any pictures or videos!

  • AudioFreeze Fascia complete

    To be able to mount my AudioFreeze PCB in a modular case I needed to craft a fascia. I decided to use laser-cut acrylic. I haven’t found anywhere in the UK that does bespoke Aluminium cutting, and, due to a kind friend, I had access to a laser cutter! I created a vector image in InkScape, a free, well-featured vector art package. It does have its drawbacks though, it’s not particular user friendly. I haven’t found an easy way to show the centre of objects, so I ended up making guidelines to show me, and hiding them in another layer.

    I came up with a design involving snowflakes, and I wanted these to be in a different colour. I covered the acrylic in masking tape, and once it was cut I painted over the top with several layers of thin acrylic paint. It wasn’t entirely successful, the paint didn’t fill the etched areas quite as well as I’d hope, but I’m still very pleased with the final result. One downside of using acrylic is that it’s 3mm thick, which seemed slightly too deep to be able to get a nut on the jack sockets as not enough of the barrel protruded. The Aluminium panels from the Thonk – Music Thing kits I’ve built were thin enough not to have this problem.

    I’ll make another demo video soon..

     

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    Vector image for laser cutting

     

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    Laser cutting the masking taped acrylic

     

    Painting onto the fascia
    Painting onto the fascia

     

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    Finished article!

  • AudioFreeze Prototype built

    After a few hours of soldering my PCB is populated and it works! There was no way of knowing for sure without building it, and as this was my first PCB I had some doubts, but thankfully it’s all good. The LEDs and corresponding resistors have yet to be added, I wanted to wait for the facia before soldering these in place to get the height right  It can be powered either via USB or from the 5V line on the Eurorack connection.

    First version of the firmware is up on GitHub. Current version has only one mode. Top red button captures a loop of audio. Pots from top to bottom control:-

    • loop window size
    • loop window position
    • pitch
    • mix with incoming audio

    Bottom red bottom currently doesn’t do anything, but my plan for the next version of the firmware is to have multiple modes. I’m thinking of a mode which has a volume based threshold for triggering the sampling, and possibly a granular delay mode. Also the ability to sample in 8 bit (rather than 16 bit) for increased loop time. LEDs are also unused currently, they will probably show active modes.

    Next up is the fascia, hopefully laser cutting that this week so expect pictures soon.

    A photo posted by @scottpitkethly on

    A video posted by @scottpitkethly on

  • PCBs have arrived!

    My first ever PCBs have arrived, possibly the first of many? Can’t wait to get the first one soldered up. After that I need to design the Eurorack panel, current plan is laser cut acrylic. Will post demos as soon as it’s made! Thanks to Hackvana for fabricating them, a highly recommended service!

     

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  • Making PCBs

    So, I’m ready to progress with my AudioFreeze project, and move from breadboard prototype to permanent module. I didn’t relish the thought of transferring the circuit to Vero board, it would be possible but fiddly. I toyed with the idea of fabricating my own (see http://www.instructables.com/id/How-to-Etch-a-PCB/), but a friend made me aware that you can get very low (10 or so board) runs of unique PCB designs factory manufactured for around £25, so roughly £2.50 a board.

    I downloaded Eagle Light Edition, PCB CAD software. It’s free for non-commercial hobbyists to use (with a maximum board size 100mm x 80mm, which is fine for my needs). To say it has a steep learning curve is an understatement, its UI is rather non-standard, thankfully I had someone very patient to mentor me and get me started (thanks Jason!)

    It took me a couple of iterations, but the board design is now finished, let’s hope it works! Just a 3 week agonising wait for them to be delivered from Hong Kong!

     

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  • GitHub

    The code (and other related files) from my projects is now up on GitHub.

    https://github.com/cutlasses/

    I think I’ll delete some of the source code from this page now as the up to date versions will be on the GitHub repository.

  • Thonking!

    I’ve decided to take the plunge (in a very small way) into the world of Eurorack. Right now, I’m more interested in creating an unusual and unique signal processing chain, than I am in creating a stand-alone synthesiser. My current plan is to try and build every module myself, either from a kit, or hopefully, in the future, from my own designs.

    I treated myself to a couple of kits from Thonk. A site well worth checking out. I built a Mikrophonie (a contact mic pre-amp) and a Radio Music, a sample player that behaves like a radio, inspired by radio-powered compositions by John Cage and Karlheinz Stockhausen. I had a lot of fun building them, even though I managed to solder some header onto the wrong side of the board (even though the board clearly states which side to use!). This mistake took about 4 hours of tedious desoldering and copious swearing to rectify. Both of these modules were designed by Tom Whitwell from Music Thing. I’ve housed these inside a Doepfer A-100 mini-case. The unfinished wood case is crying out to be screen-printed, but that’s a project for another day! They both worked pretty much first time, which I was fairly surprised and pleased by. I’ll post up some demos when I have some more interesting things to run them through.

     

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