Prioritizing MIDI channels

[Ari]

I imagine everybody here with a SC-55 or compatible is aware of the low polyphony of these devices. I think it's the biggest drawback of the SC-55 line of products, and every once in a while, when I play a piece from my extesive collection of midi files, I hit one that although sounding great, it loses a lot of notes which makes the theme virtually unlistenable using my SCD-15 (which has an extra 4 note polyphony and still fails miserably when it comes to some themes).

I use vanBasco's MIDI player to playback midi files, and it shows all the notes being played at any given time. this allows me to judge, more or less, how many notes are being played simultaneously, and to my surprise, I've noticed that with some themes, I start losing sound with a rather low count of notes, while in other cases, I get a very high count, and yet, I hardly lose anything.

I've heard it's possible to give certain channels a higher priority, and by that keep the more important notes of the theme. Does anybody know how one does it?

[Tom]

Through SysEx, you can create a "reserve" that will give some channels priority over others -- just like with the MT-32.  But I've not done it and don't think I have any SysEx code around for it.  It depends on how many "elements" (SC) or "partials" (MT-32) are being played at the same time, not how many notes.  Since different instruments use different amounts of elements or partials, sometimes many can play at once, while at other times, only a few can play.  Your SCD-15 tone map shows how many elements each sound uses.

[Ari]

Yeah, I've seen refferences to these 'elements'.
Just out of curiousity, how many elements is the SC capable of simultaneously? 28 as well?

[moturimi1]

Yeah, I've seen refferences to these 'elements'.
Just out of curiousity, how many elements is the SC capable of simultaneously? 28 as well?

The Original SC-55 can play up to 24 voices/elements.
The SC-55 MKII can play 28 voices/elements.

The following instruments use 2 voices per tone:
- Honky tonk (also Honky Tonk w)
- Detuned EP1, E.Piano 1v
- Detuned EP2, E.Piano 2v
- Coupled Hps, Harpsi.o
- Detuned Or1, Organ4
- Detuned Or2, Organ5
- Organ3
- Church Org2 & 3
- Accordion French and Italian
- Bandoneon
- Nylon Gt.o
- 12-str. Gt.
- Chorus Gt.
- Feedback Gt.
- Synth Bass2 & 4, Rubber Bass
- Orchestra
- Syn. Strings3
- Syn. Strings2
- Orchestra Hit
- Trombone2
- French Horn and French Horn2
- Brass2
- Syn. Brass1 & 3, Analog Brass1
- Syn. Brass2, Analog Brass2
- Bottle Blow
- Shakuhachi
- Square wave
- Saw wave, Doctor Solo
- Syncalliope
- ChifferLead
- Charang
- Solo Vox
- 5th Saw
- Bass&Lead
- Fantasia
- Polysynth
- Bowed Glass
- Metal Pad
- Halo Pad
- Ice Rain
- Soundtrack
- Crystal
- Atmosphere
- Brightness
- Goblin
- Echo Bell, Cho Pan
- Star Theme
- Sitar 2
- Taisho Koto
- SFX: Stream, Bubble, Bird, Wind Chimes, Car-Crash, Jetplane, Straship, Burst Noise, Applause, Explosion.

[Zemus]

The SC-55 has a polyphony of 24 voices. I've also noticed another weird problem. When I played back some of the MIDIs recorded from Sam & Max, not all notes played even though it was well within the limits of the polyphony. However, in the game the notes were played...

If I remember correctly, the first channel has the highest priority and the last one has the lowest priority. Change channel numbers may help you without having to figure out the sysex.

[HondaSiR]

Taken from my SCB-55 manual (page 6):

When the number of Voices being used exceeds 28, some of the notes that should be played could be cut. To avoid "losing" important notes, there are two features you can use to insure that a particular Part has all the notes it is supposed to.

Part Priority:

When the SCB-55 receives performance data which request it to produce more than the 28 voices available, priority is given to producing the most recently received note messages. Those that have been sounding for a while will be cut, in order, starting with the oldest ones, and the ones that are assigned to the Parts with the lowest priority.

Part Priority Ordering:

10 > 1 > 2 > 3 > 4 > 5 > 6 > 7 > 8 > 9 > 11 > 12 > 13 > 14 > 15 > 16

For this reason, consider a Part's importance (bass, chords, melody, etc.) carefully when assigning it to a Part on the SCB-55.

Voice Reserve:

The Voice Reserve function allows you to specify a minimum number of Voices that will always be reserved and made available for certain Parts. This becomes effective in instances when the total number of Voices that have been requested exceeds the capacity of the unit.

When shipped, the following settings were made for Voice Reserve:

Part 1:          6
Parts 2-10:    2
Parts 11-16:  0

As Voice reserve for Part 1 is set to "6", Part 1 will always have at least 6 Voices - even when all Parts combined are requesting more than 28 Voices. In other words, with Part 1 set this way, all the notes that it should play will be played faithfully (as long as the sounds assigned to it do not use more than 6 Voices).

[Ari]

So switching between channels can give a higher priority to "more important" instruments... interesting... I'll have to experiment.

Thanks guys!