MT32-Pi: Glitchy upon loading certain DOS games until Soundblaster FX kick in

[Jimiga]

I just received my MT32-Pi, and WOW! This thing is amazing. It's working almost perfectly, with the following hitch.

ISSUE:
On some DOS games (Monkey Island 2, Day of the Tentacle), the music starts in a very glitchy / distorted way, until the first sound effect kicks in at which point it becomes perfect. It's as though the sound effect starting corrects the issue with the music.

MT32 Audio working perfectly on X68000 core, Amiga, and ScummVM

EXAMPLES:
Monkey Island 2, glitchy start to music over Lucas logo, then perfect as soon as Guybrush speaks to the monkeys. This in the talkie version. In the non-talkie version, music stays glitchy throughout and never corrects.

Day of the Tentacle, Glitchy over logo until we hear the first sound effects over the intro, then perfect throughout

Same on loading a saved game in the talkie Monkey Islands 1 and 2 - Music distorted until someone speaks, then perfect.

SETUP:
MiSTer with good Meanwell PSU
ExoDOS Top300 Dos games pack, updated
Pi3B+ with up to date MT32 ROMs & all corrections made per the guide
8BitsForever MiSTress A600 I/O board

Thanks in advance!

[aberu]

Sounds almost like an issue with the USB cable, this kind of thing can happen with latency spikes.

If you are using flynn's top300 pack, have you ran the updater script for it --> https://github.com/flynnsbit/Top300_upd ... and-update ?

[Jimiga]

Thanks for your reply - I did run the updater last week right after downloading the pack.
THe USB lead is the short one that came with the board from MisterFPGA.co.uk, so I think that's good.

I'll try running the updater again... just didn't want to lose my existing saved games and wasn't sure if they'd be wiped!

[Malor]

I just double-checked, and my MI1 and 2 are flawless.

What flavor of Pi are you using?

This is a low-probability fix, but one reason for super-scratchy, nasty sound is the undervoltage detection on the Pi being triggered. No matter how big your power supply is, the Mister will only emit so much amperage out the user port, so a plugged-in Pi will often detect an undervoltage condition, and will throttle itself heavily. There's actually enough power to run it fine, so you can disable that setting in the ini for the Pi's card. (I don't think there's any easy way to edit it remotely, you have to yank it and change it on a desktop or laptop.)

Another possibility is that your Pi isn't quite running fast enough, and might need to be overclocked a smidge.

Yet another possibility is that there's something wrong with the cable. The timing on the MT32Pi is extremely tight, and if the cable is even a tiny bit out of spec, it can cause problems.

edit: it kind of sounds like a mixer bug, or maybe the SB16 emulation wobbling the voltage a little and then the Pi speeding up because it doesn't detect low voltage anymore. Maybe.

[Jimiga]

Thanks @Malor
Pi3b+

There is one odd thing re the config.txt instruction. The guide says if you see a low voltage warning, to add
avoid_warnings=2
above the [Pi3] line

When I do so, I still get the low voltage warning

If I add the same line below the [Pi3] line this warning goes away and things function very near perfectly, this issue being the only hitch .

My cfg.txt file looks like this:

Code: Select all

# Remove delay and use cutdown start_cd.elf/start4cd.elf for slightly quicker boot
boot_delay=0
disable_splash=1
force_eeprom_read=0
gpu_mem=16
disable_overscan=1

# Uncomment the following line if your HDMI audio extractor isn't outputting any sound.
# This forces HDMI signalling in case your device is detected as a DVI device.
#hdmi_drive=2

# Uncomment the following line to disable undervoltage/temperature warnings and throttling.
# WARNING: Possible instability; use at your own risk! Use a heatsink!
#avoid_warnings=2

[pi02]
arm_64bit=1
kernel=kernel8.img

# Uncomment the following to overclock the Pi Zero 2 W to match the performance of the Pi 3B
#arm_freq=1200
#over_voltage=2

[pi3]
[b]avoid_warnings=2[/b]
arm_64bit=1
kernel=kernel8.img

[pi4]
arm_64bit=1
armstub=armstub8-rpi4.bin
kernel=kernel8-rpi4.img

# Optimized frequency settings for lower energy use/temperature on Pi 4
arm_freq=600
arm_freq_min=100
gpu_freq=100
over_voltage=-16
over_voltage_min=-16

Lastly - the pi has no heat sink until it arrives tomorrow!! Not sure if this is could cause this issue - I'm only using in short bursts til then.

[Malor]

Those settings look fine. I guess heat could be a problem, so pointing a desk fan at it until the heatsink shows *might* help. Probably not, but it can't hurt.

It's definitely working right here, so I'm thinking there's something not *quite* right with your hardware, somehow. A slightly bum cable is one possibility. Just in case, maybe try carefully reseating both ends?

edit: btw, you were correct to move the avoid_warnings=2 line under the [pi3] header.

[Jimiga]

Thanks very much for your input - I'll keep experimenting!

I checked the cable seating and still have the issue. It's really just three games after a lot more testing, Monkey Is.2, Day of the Tentacle (both with those glitchy starts), and Sam & Max which just doesn't play Midi audio at all.

In ScummVM, all three games work perfectly in MT32, and every other core is flawless, which is making me think it's perhaps something in the A0486 install / software.

It's very usable in it's current state, it'd just be nice to work out this one hitch. I'll get there! I'll report back.

A second cable is on order, longer but still on the 'approved and tested' list, so I'll see if that makes a difference.

[Malor]

If you haven't already, try the versions in the Top300 collection. That's what I've been using here. When I choose the MT32 plus Soundblaster option on launch, they've been flawless.

[Jimiga]

Thank you - those are the versions I'm using in the VHD. Nice to know they're solid.
I also just re-ran Flynnsbit's updater script for the top 300 pack successfully, and reinstalled the software for the Pi on the SD card side. Issue still persists though.

New cable and heat sink should be here shortly, so I can try those too. Appreciate your efforts in helping out!

[Jimiga]

Just curious @Malor, does Sam & Max AO486 work for you? I choose the option for MT32, but with that game only get the standard sounds. It does say loading sounds at the start, but I definitely don't hear the MT32 at all there.
Thanks!

[Malor]

I'm running an older Top300 that has disk corruption; I need to redownload it. On my version, if I choose Soundblaster or MT32, I get the correct music. I do not, however, get any voices with either choice. Characters do a lot of lip-flapping, but no sounds come out.

At least on my older Top300, Sam and Max appears to be pretty badly misconfigured.

[Jimiga]

Thanks for the update, good to know, that one might be a reinstall as things don't seem quite right for either of us there.

[Jimiga]

Update - tried new cable - same results.
Monkey Is. 1 & 2 talkie versions, music is glitchy until a voice / kicks in, then it resolves and is perfect.

I actually have another mister with the standar analogue I/O board which I'll check against this one to see what results I get and report back here in case it's helpful.

Thanks!

[Malor]

Boy, that is a *weird* bug. Hope you figure it out!

[NightShadowPT]

Hi,

Did you progress on your troubleshooting attempt?

Where are you getting the MT32-pi sound coming from? The MT32-pi jack, or loopback through the MiSTer?