New Gadget Madly In Hope

A blog about my iPhone dev efforts

19 February

Polyphonic Microtonality

I'm doing an experiment in PolyHarp that might make its way elsewhere.

Here's a quick summary of the problem:
MIDI now officially supports a standard called MPE, the idea of which is to bring more features to individual notes that are normally assigned to channels.
For instance, pitch bends, CC values, and the like. This gives lots of Polyphonic Expression where it wasn't supported before. MPE works in a backward compatible manner by leveraging note assignment to put each note on its own channel, with all expression (like pitch bends) preset for it.

This is flexible, but it subject to subtleties associated with note assignment. MPE also divides the 16 MIDI channels into "zones", with one channel per zone reserved to receive commands and behave like each single channel normally would, but applied to all the channels in that zone.
MPE software sits on top of MIDI and if you have a legacy device or set of devices that can do non-OMNI mode polyphonic multi-timbralism, like some old General MIDI synthesizers, you can play some microtonal music on them without any firmware changes.
While this is a powerful general solution, it has a big problem: it maxes out at 15 note polyphony.

PolyHarp is a polyphonic microtonal synthesizer. That means each virtual string can be set to a pitch that has nothing to do with the 12ED2 system that is hard coded into MIDI (and much other western music). PolyHarp's internal synthesizer doesn't care about 12ED2, it'll play any old pitches. But when acting as a MIDI controller, it has to be more careful. I will probably add MPE support, which will allow some of the features that Polyharp already supports, like different sounds and behaviors controlled by different string areas. But beside microtonality, PolyHarps other big feature is massive polyphony. This is what lets it detune strings or make super dense chords. Limiting it to 15 notes is indeed limiting.

So I came up with another compromise that I call MIDI192. Like MPE, it channelizes notes to get the pitch bends that apply to it. Unlike MPE, it cannot play any microtonal pitch perfectly. MIDI192 lets you set up a subset of the 16 channels and assigns each channel to a degree of an equal division of a semitone for each of the number of channels it uses. The subset is so it can exclude some channels that don't care much about pitch anyway, like channel 10, used often for percussion. When using all 16 channels, instead of 12 notes per octave, you get 192 notes per octave (whence the name). This means that for an arbitrary tuning, you are within 100/16 cents of the real pitch, 6.25, and actually because it rounds it, its more like 3.125 cents or better. While not perfect, it's pretty good, and has no polyphony limit other than what the synth can handle. And for some equal temperaments that are multiples of 12, like 24, 72, 96 , it IS perfect, at least in theory . Every channel that's used gets a pitch bend sent to it when the MIDI192 system is chosen. This amount is based on how much a "real" pitch bend, from the wheel, should bend. By default, I'm using 6 semitones. A smaller bend will make the preset bends a little more accurate. There's some tweaking that goes on when a real pitch bend come in - it adds the preset bend to the new bend and transmit it to all affected channels. Because of the polyphony, you can't bend individual notes though.

MIDI192 doesn't have a zone system like MPE, but I could be able to block out channels into zones similarly by using channel masks, essentially making less accurate pitch to get multi timbral. We'll see!

I've put a test version into PolyHarp, which would be an option when you set up MIDI - either good old MIDI, or this new system, (or MPE...). You'd be able to set the bend distance and the channel mask as well.

Here's a video about it! https://www.youtube.com/watch?v=-ebJZRZFLFg
More as this develops!
15:02:52 - jhhlnet - No comments yet, click here to add one

24 January

PolyHarp 1.0.5

PolyHarp got released a while ago, but meanwhile little bugs keep popping up in the MIDI department.
Most of those have to do with the fact that a lot of MIDI synths would like a note off after a while. A note off is really kind of independent of a note on. PolyHarp has a timer that starts with note ons to shut them off after a while . The natural way to turn them off is when they are damped or run out of energy. You can't test the energy of a MIDI note, which is why PolyHarp just scheduled a Note Off.
There was a bug where I was scheduling too many note offs that I fixed a few weeks ago, but there's a more subtle bug:
Play one note and play it again .. the first note's scheduled note off would shut off the new note prematurely. I've now fixed this in PolyHarp 1.0.5
16:36:13 - jhhlnet -

13 December

PolyHarp 1.0.1 released

PolyHarp was released a few weeks ago, and I already have an update for it, which fixes a few typos. I'm continuing to rewrite the instructions - much of which refers to outdated UI and features!

PolyHarp provides a lot of control in its controls now: you can make the strings play with a touch, bend, retune, and be confined to string areas onscreen. You can control the chord bars from MIDI in or Audiobus Remote.
The chords can be made out of all kinds of intervals, repeat, and be displayed out of order. The string areas can be any four-cornered shape, twist and overlap. They can be colored in harmonious ways.


Go check it out at http://polyharp.com
10:32:47 - jhhlnet -

07 November

PolyHarp 1.0.0 in Beta

I've been trying to get a beta out of PolyHarp for months - there was some misunderstanding of some sort in its Info.plist file that kept it from being accepted. Finally that's been cleared up!
There's a list of stuff I want to fix in it, and I hope my beta crew will find some more.
00:44:30 - jhhlnet -

28 March

PolyHarp is coming

New App I am working on
My guess is that very few people read this - they are all out on FaceBook .. but anyway, I'm working on a new app very feverishly . (I should be working on old apps, but there are things I want to try out).

Anyway, it's called PolyHarp, and it's kind of a update to my old Amiga program LYR. LYR was an Amiga based autoharp simulator.
It played MIDI synthesizers and had some pretty bizarre chords and features, including a strum sequencer.But LYR never got to a stage where it was user configureable.

The main differences are:
- iPad only .. it's too big for a iPhone.
- synthesized, not MIDI. that means chords can be made of any musical intervals, not just those in a 12EDO scale.
- "strings" on the harp correspond to the strings of the chords.
- of course any chord setup can be transposed.
- you can make up polyharps with a great number of chords
- you can layout the chord buttons all over the screen
- a chord bar is a collection of intervals which themselves are transposed by a relative interval, which is resolved to a base "key"
- strings are resolved within an adjustable frequency range.

Thus, if your Base key (frequency really) is an F, a "IM" chord becomes an "FM", a "V7" chord is "C7". but there are vast numbers of new chords to be made,
like ones with other equal temperaments, or just ratios, equal divisions of other intervals, or merely cents.
You can compare variations on the same chord. The chord bar intervals are specified with the good old tonality spiral used in Droneo.

Audiobus support will help it along!
00:34:30 - jhhlnet - No comments yet, click here to add one