Published on September 20, 2024 2:30 AM GMT
I had a great time playing Amherstlast night with Cecilia, except for thekeyboard gremlins. I just got a new keyboard (more on that later!)and it worked great when I tried it at home. At the dance, however,there were strange crackles. Even weirder, when I played the highestnotes on the piano, I got a very small amount of phantom bass, maybefour octaves down. It got louder and quieter, as I turned the keyboardup and down or played at different volumes, and if I turned down thevolume on the keyboard it went away. MIDI output, which is a key partof my rhythm stage setup, was totally clean.
I was really very confused. I thought maybe this keyboard didn't havegood enough electrical shielding, and having my little stage computervelcroed to the keyboard might be causing it? In support of thistheory, turning off the little computer did fix it. But moving thelittle computer to the floor, where it should not have been able togenerate meaningful interference, did not. After trying a lot ofthings, I eventually realized that disconnecting the MIDI cable wasenough to fix it.
This is one of the main differences between this keyboard and myprevious one: it's USB MIDI instead of 5-pin MIDI. But I had used mysystem with USB MIDI before, with no issues. It was reallyfrustrating, and I was baffled. I took a video:
This evening, I tried to reproduce it. The same setup as I had onstage did trigger the issue. Connecting it to my laptop, however, didnot trigger the issue. So probably not a keyboard problem, andinstead some thing my little stage computer is doing.
I thought maybe I was sending MIDI back out, which should never havepreviously mattered because I never used to connect the MIDI cable inthe other direction. I started installing tshark todebug, when I realized the problem:
My little box is set up to do two things:
If it detects it is being used as a MIDI router, itroutes MIDI and synthesizes audio. This is triggered by noticing thatMIDI devices are connected.
If it detects, it is being used as a bass whistle,it interprets audio and generates bass. This is triggered by noticingcertain soundcards being connected, ignoring both the built-in one andthe one I use in MIDI routing mode.
In this case both of these conditions were met. I was using it as aMIDI router, but also the new keyboard presents itself to thecomputer, among other things, as a USB audio device suitable for basswhistling. When I played high notes on the keyboard they were beingsent out as MIDI, but they were also being sent out as USB audio,which was going into my bass whistle logic. If the note was in thesame range as my whistling, it would dutifully transpose it down fouroctaves and send it back out via the same device, the keyboard, andfrom there to the hall sound system on the keyboard channel. Thecrackles are something the whistle sometimes does when it issufficiently confused about its input.
What makes this especially unfortunate is that I have completely movedon from ever using my little box for bass whistle. Instead, I have anarduino-based system, which Ilike a lot. The fix turned out to be just disabling the bass whistlecode I should have removed a while ago. No more gremlins!
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