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The MIDI Forum

  Tuesday, 08 November 2022
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I'm about to midify a Hammond bass pedal (25 keys). I'm wondering what usual scan rates for musical instrument keyboards are?
It is the intention to always find the latest pressed key and possibly all other pressed keys. The keys are arranged in a matrix 4x8, like in the attached scheme.

Also I don't know whether this is the right forum to discuss such issues.
Christoph set the type of the post as  Technical Question — 3 weeks ago
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Yes, this is the correct place to ask. I hope someone knowledgeable about hardware will respond.
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Both classic MIDI and USB MIDI have a latency of about one millisecond, so it does not make sense to have a scan interval much shorter than this.

You want to avoid noticeable jitter. Bass pedals are not played very quickly, so you might be able to get away with a longer interval.
3 weeks ago
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#16534
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Both classic MIDI and USB MIDI have a latency of about one millisecond, so it does not make sense to have a scan interval much shorter than this.

You want to avoid noticeable jitter. Bass pedals are not played very quickly, so you might be able to get away with a longer interval.


But isn't the overall latency important as well? The duration from the key press to the detection shouldn't exceed a millisecond or so either.
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Yes. But reducing the overall latency from 1.4 ms to 1.2 ms might not be worth the effort.
2 weeks ago
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#16557
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Thanks for the ideas. Actually I'm seeking for a place for discussing the scanning algorithm (software wise) a bit more in depth.
Do you think I should proceed here? Scanning a musical keyboard might be different from scanning a calculator or computer keyboard.

Especially when considering situations where you play legato and the last note is triggered while the second but last still is pressed.
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Asking here is OK.

There's nothing special about legato; only the device that actually generates sounds has to decide whether two notes are near enough to be legato.
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