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Cart #22439 | 2016-06-07 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA
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I'm not sure if this is documented, but I accidentally discovered some neat features of the audio engine while playing Jelpi in corrupted mode.
I noticed that sometimes the music would be affected in a way that couldn't be possible with just the editor. By experimenting a little further I discovered a small section in memory dedicated to effects:

0x5f40: play channel twice slower
0x5f41: a very short delay (cheap reverb/unison simulation)
0x5f42: distortion (rounds the output waveform to min or max depending on which is nearest)
0x5f43: low-pass filter

For each of these values, bits 0 to 3 correspond to channels 1 to 4 respectively (for example, poke(0x5f42,6) will apply distortion to channels 2 and 4). Bits 4 to 7 seem to be unused.

With that in mind, I decided to code a little program that would apply random effects to random tracks until the song becomes completely destroyed. Here's the result (the song is pretty cheesy I have to admit).
Enjoy :)

P#22440 2016-06-06 22:50 ( Edited 2016-08-23 03:41)

whoaaaa secretss yesssss!!!

P#22441 2016-06-06 23:03 ( Edited 2016-06-07 03:03)

Yay!! Awesome!! \o/

P#22442 2016-06-06 23:37 ( Edited 2016-06-07 03:37)
1

This is extremely cool and useful, nice find! I can already think of many fun ways to make use of this, like applying a low-pass filter on the music while in some sort of inventory screen or reverb in caves.

I'm loving all these undocumented features being discovered, every new find is more exciting than the last.

P#22460 2016-06-07 15:13 ( Edited 2016-06-07 19:13)

This is very cool and all but I'm here to just appreciate that awesome music. :P

P#22461 2016-06-07 15:18 ( Edited 2016-06-10 02:57)

Kickass spritework, qbicfeet. Tell me you're doing a Spelunky demake. Or at least a La Mulana one. :D

P#22535 2016-06-08 17:58 ( Edited 2016-06-08 21:58)

This is awesome! are any of the effects likely to make it in to the tracker part of pico8?

P#22546 2016-06-09 06:57 ( Edited 2016-06-09 10:57)

Another "secret" thing found ^^
the screen video mode, the stats on music, the mouse, now that.. :D

P#22573 2016-06-09 21:14 ( Edited 2016-06-10 01:14)

Loving this.
I actually encountered this bug while poking the Hello demo a bunch and then going into the edit screen and playing the song from there. I was searching for the memory addresses to poke since! xD

P#26949 2016-08-15 11:08 ( Edited 2016-08-15 15:08)

Is there a place we're documenting all these 'secrets'?

P#27230 2016-08-22 23:41 ( Edited 2016-08-23 03:41)

Hi, I'm fairly new to Pico-8. There are a lot of interesting sounds coming from this cart. It's nearly 8 years since this thread was created. Are these sounds now possible straight out of the latest Pico-8 music tracker? Or are these memory pokes still relevant to generating sounds that would otherwise be impossible in the tracker?

P#146088 2024-04-08 17:09

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