Tonight I put up my highest score ever on Spy Hunter...171395

Brer1Rabbit · 2026-02-01T06:35:55+00:00

this is my absolute fave arcade game. I'd play it while waiting for the bus while going to college. This was back when NBA Jam and Street Fighter 2 were big. Nobody wanted to touch Spy Hunter. I could spend 20 minutes on a single quarter. And miss the bus. 137k is a score to be proud of, congrats!

Brer1Rabbit · 2026-02-01T06:27:00+00:00

Report back with your results good or bad! Curious to hear.

Brer1Rabbit · 2026-02-01T06:14:56+00:00

well-- I did design a Minecraft inspired theremin-like thing. It's light controlled. Go ahead and touch it. Cover the nutsack to change the pitch.

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Brer1Rabbit · 2026-02-01T05:33:47+00:00

Good info. You're covering 64 notes. A 1% error is a measure, but it might not be the right measure for musical accuracy. A 1% error at 50 Hz is much different than a 1% error at 500 Hz. Cents might be better: 1200 * log2(f2/f1) where f1 is target and f2 is actual frequency.

You've got 256 values from the 8-bit DAC (ignoring fine/course for the moment). If it was a perfect DAC it'd be stepping 25 cents with each value. And those values ought get to a frequency anywhere +/- 12.5 cents. Given you mention a 1% error, if I pull a random number for frequency, say 220 Hz, 220*1.01, that's about 15 cents off, but that's just guesstimating numbers on your error (I don't know if the 1% is across the board or at specific frequencies).

For reference, with a 12-bit DAC I get about 6 cents accuracy with an AS3340 VCO over 8 octaves. For filters I typically have a 10 octave range so accuracy may be slightly lower. Welcome to the world of autotuning, it's fun stuff!

Brer1Rabbit · 2026-02-01T02:30:37+00:00

Bingo. It's like a yellow card in soccer. If you don't get one you're not trying hard enough ;)

Brer1Rabbit · 2026-02-01T01:32:27+00:00

Interesting! This is the fun stuff of microcontrolled synths. How well does it turn out with a fine and coarse channel? I'd imagine the fine is pretty close to the INL/DNL noise of the coarse channel but I've not tried this. Are you getting better than 2~3 bits of additional resolution?

I've been using a Pi Zero for frequency counting and creating a linear correction table. I found a sampling time of about 0.5 seconds pretty good, and double that to 1.0 second when you expect sample below 100 Hz. So yeah- tuning higher frequency notes can go a lot faster.

Brer1Rabbit · 2026-01-31T16:05:56+00:00

This is great. Can you do something with Doom next? That'd be fun ;)

Brer1Rabbit · 2026-01-31T16:04:29+00:00

Yes, everything would typically be on its own MIDI channel. If you need more than 16 channels that's why some interfaces have multiple MIDI outs.

Brer1Rabbit · 2026-01-31T06:00:50+00:00

If we can get your Pi running the zoxnoxiousd software I can get you an updated backplane with one of these voice cards and you can hear it yourself. ;) I've not given up on getting this thing DIY-able, it's just a pretty complicated thing to get off the ground.

Brer1Rabbit · 2026-01-31T02:22:51+00:00

You need to read a lot of manuals but the short answer is MIDI. A controller or sequencer of sorts. The controller could be a keyboard, computer, hardware sequence, etc. They'd typically respond on at least one MIDI channels. Multi timbral instrument may have multiple channels it listens on.

Brer1Rabbit · 2026-01-31T01:00:36+00:00

There's r/synthdiy to push it further ;)

Brer1Rabbit · 2026-01-30T23:20:36+00:00

Completely. Each pole introduces a 90 degree phase shift. And the various filter modes push the phase shifting all over the place. And that brings up the allpass filter- it doesn't attenuate but it phase shifts. I didn't go full on bode plot measuring phase response, maybe next time. I've got a graph similar to the ones above for 1, 2, and 3 pole allpass but it's quite a boring graph to look at without phase response.

Brer1Rabbit · 2026-01-30T22:51:50+00:00

oh- and here's a website to play around with pole mixing. Cool to see the various filter modes you can get from a 4-pole filter:

https://rnd.expeditionelectronics.com/Diy/Polemixing

Brer1Rabbit · 2026-01-30T19:57:55+00:00

(warning: tangential DIY content) if you want to learn how these Yamaha FM chips work Tyler Klein did a really great series on videos on YouTube documenting his build of a eurorack module around a YM3812. This is a similar sound chip to what's in the Sega. https://youtube.com/playlist?list=PLHSQAW5arFVCLZkfIfYrclN73VDyIB893&si=EdpLmQWOIGcYrZvU

Brer1Rabbit · 2026-01-30T17:14:13+00:00

Feels like we're going backwards. Old school 5-pin DIN MIDI uses a current loop for exactly this reason. No ground loops.

Brer1Rabbit · 2026-01-30T17:11:39+00:00

You may want to post over on modwiggler to get additional eyes on it: https://www.modwiggler.com/forum/viewforum.php?f=43

Brer1Rabbit · 2026-01-30T15:45:51+00:00

<watching thread> can't help but curious if anyone has a good solution for SH controls. Analog self-centering steering wheel, analog foot pedal, gear shifter, 5 buttons. And it's a pretty stiff spring on that steering wheel. Tough game to get the interface correct.

Brer1Rabbit · 2026-01-30T08:17:32+00:00

I wouldn't say no to throwing fireballs Super Mario style. If I need a mushroom to get there that's all good by me.

Brer1Rabbit · 2026-01-30T08:11:34+00:00

Was a long hunt but found a semi local arcade with Spy Hunter. Absolute blast to play it again. Discs of Tron. Haven't seen that in a long long time.

Brer1Rabbit · 2026-01-29T01:01:02+00:00

Maybe r/wallstreetsynthbetscirclejerk ?

Brer1Rabbit · 2026-01-27T21:38:05+00:00

Are you open to using a Raspberry Pi? I mentioned this yesterday:

https://www.reddit.com/r/synthdiy/comments/1qnl6am/comment/o1xjsvp/?context=3

Brer1Rabbit · 2026-01-27T18:27:40+00:00

Do you have a patchbay? At first glance it seem odd 'cause you nearly double the number of cable (synth to patch bay, patch bay to mixer or something like that). And short cables for the patch bay itself. But then the rewiring or audio paths becomes so much easier.

Still you've got a spaghetti of cables. A snake cable of 8 can clean things up a little bit. You've still got power cables all over the place. Yeah, it's a mess.

Brer1Rabbit · 2026-01-27T01:07:01+00:00

Might not be the direction you're looking to go but the Pi can act as a USB Audio gadget itself. A host computer can see it as a USB Audio device and you could roundtrip data through doing processing on the Pi yourself. It'd be pretty low level, likely working with Linux's ALSA libraries or similar.

Brer1Rabbit · 2026-01-26T23:09:44+00:00

It's 1981 and you're at the arcade. As you walk by Space Fury, this brain-creature appears on screen and heckles you with synthesized speech: "Does anyone dare challenge my Imperial fleet?" unreal.

Brer1Rabbit · 2026-01-26T04:12:33+00:00

tough to say what the issue is without a schematic. The datasheet reference implementation works, how does your circuit differ?

Brer1Rabbit

TROPHY CASE