MIDI IN

This week has mostly been spent working on mono mode but it's not yet ready for a demo. Components have arrived for the next hardware version (which is going to look great) but the boards haven't turned up yet. So the update this week will consist of a piece of music I put together partly to demo MIDISID's General MIDI mode, and partly to have fun playing with a new instrument I've just put together. Rakits are a fab introduction to the world of modular synthesis, I love my baby8 and atari punk console. I had the good fortune to meet the 'MakeaRakit team' at emfcamp a couple of weeks ago and couldn't resist buying some more kits. What attracted me to the Cracklebox was partly the method of playing it and partly the unpredictability, which goes against my nature completely.  You have a little control but really don't know what you're going to get. Something quirky and slightly sinister was required for a backing groove. A 3+3+2 (which has a waltz fee...

In one respect it doesn't seem as if we're very much further on than last week because what I have to demonstrate are the parameters within polyphonic mode. If you liked the animated visualisation of the ADSR envelope last week, then this is more of the same, but this time a proper run-through of all of the parameters that make the SID the legendary synthesiser on a chip that it is. We now also have animated representations of the Pulse Width, Pulse Width Modulation, Filtering, Vibrato. Tuning is also incorporated with fine and coarse controls.  In other respects we've made leaps forward and the finished product seems closer. I've done a lot of work on the boards. As the output circuit really needs 9v, I've added a 9v jack / battery clip and regulator and put all the ports neatly at the back.  Incidentally, with the audio circuitry powered from a good 9v source and the chips powered by regulated 5v from that. the audio output is way better than when driving the whol...

You may have seen this image, posted by Twitter user Threatening Music Notation .  [ Link to Youtube video in case you prefer viewing rather than reading.] The first problem is that the notes are labelled incorrectly. Or mostly incorrectly. The second is that the notes aren't spaced correctly. Or are they?   Glossing over the labelling, could the designer have intended this to be a set of notes, spaced differently from the way that we usually do? This idea intrigued me, and I set about finding a way to play the notes "as written" We have to make some decisions here. It does look very much as if the spacing is four of their notes where we would usually write three, So I'm going to take that E (labelled D) G (correctly labelled) and B (labelled C) as anchor points, and fill in the frequencies from there. I'm familiar with the table of values for the SID sound chip in the Commodore 64, this gives the values that we pass the SID to get particular frequencies.  From t...

This week I've continued to work on the menu / controls and have added something that I'm really pleased with. I've made a video demonstration, with commentary - below the video is a transcript with pictures in case, like me, you prefer text and images. (If you need background, the SID is the sound chip from the Commodore 64, it's a 3-oscillator synthesizer with many features; wave, envelope, pulse width, filters, ring modulation. I'm driving it here with a microcontroller and writing the software to turn this into a midi sound module / musical instrument.) I'd like to demonstrate a feature that I've just added, which I'm really pleased with. Today I've got a MIDI keyboard beside me, plugged into MIDISID using the DIN socket. Its output is audio and I've got that plugged into a portable speaker. I'll be using the polyphonic mode, which puts the same sound on all of the SID voices available and allows you to play up to (in this case with 2 sid...

 I've spent a little time getting MIDI output from my little theremin. I thought it would be possible using pitch bend to adjust the frequency between the midi notes (semitone steps). Good news, this is working well. Bad news, I hadn't considered the envelope of the notes. The 'steps' you hear are the attack/decay of each new note beginning. I hadn't considered this issue.  It might be possible to use a sound that has no envelope. There may still be a very slight click between notes, but shouldn't be too noticeable.  However, I don't want to require a specific type of sound. It  would be ideal if it could work with any sound patch. Is it necessary to 'note off / note on'  from one semitone to the next? Just sending note ons doesn't work because you end up with a cacophony of each note still sounding.  I've done a little reading and it's not looking promising. There is a concept of portamento in midi, but this isn't standard.  More rea...

I've started to realise that the quality of the sounds that I build into MIDISID will have a large effect on its appeal. It will be fun to implement some of these: What should 'Goblin' sound like?? These aren't my names, they're part of the General MIDI specification , anything that implements GM should implement all 127 of these sounds in some way.  I've been away for most of this week  but while away,  the board I designed last week has arrived! As with the main board, this is a very quick and dirty iteration, just to get components off the breadboard and securely soldered together while I work on the firmware. This little demo of the menu system is the same as the one I made last week, but here we can see the 2-board system I now have planned. There will be a third layer which is a face plate just below the knobs with a cut-out for the screen. Those three boards could be sandwiched for a nice-looking unit, or separated to fit into any box you like. Alternati...