lr-atari800 sound is distorted, while atari800 sound is clean

n2185x

Pi Model or other hardware: Raspberry Pi 4, 2GB model
Power Supply used: CanaKIt USB-C 3.5 amps
RetroPie Version Used: 4.6.9
Built From: Pre-made SD card image from RetroPie web site
USB Devices connected: Keyboard, mouse, Atari joystick via Monster Joystick adapter (shows up as "Van Ooijen Technische Informatica Joystick" in "lsusb" output)
Controller used: Atari 800 joystick (keyboard for Emulationstation navigation)
Error messages received: none
Emulator: lr-atari800

Updates and upgrades performed via retropie-setup.sh

Sounds emitted by lr-atari800 are distorted. In particular, it sounds like there's something like a 15 Hz signal embedded it or something, but the volume of the distortion is proportional to the volume of the sound itself, so it's almost as if there's a modulation being applied or something.

The problem is most evident if you perform the audio self-test when the emulator is in 800XL mode. The audio from "atari800" is clean, while the audio from lr-atari800 is not.

The audio output is via HDMI. Note that I've not found any other emulator that seems to exhibit this issue, including other "lr-" type emulators.

If you have trouble replicating the issue, I'll be happy to supply configuration files and other such things.

mitu

I think you're stumbling upon this issue, which has been fixed in the standalone emulator, but not ported to the libretro core (lr-atari800).

n2185x

@mitu Nope, that's not it. I applied the pull request diff (https://github.com/libretro/libretro-atari800/pull/44/commits/da7893488b18f18282f2f3a121bb4c13df947a99#diff-c32948c89abf417f4eddbb951f440f7031ad98a2588c68b63b064bef299ffbd3) for that bug to the current lr-atari800 source and the end result is exactly the same as far as the distortion goes. It cuts the volume in half but has no effect otherwise.

n2185x

@mitu Also note that the bug you pointed at is with respect to a constant low hum of around 95 Hz, while the problem here is a roughly 15 Hz modulation of emitted sound. The emulator is silent when there's no sound playing, and the amplitude of the distortion is proportional to the amplitude of the sound, so quieter sounds have quieter distortion, in proportion to their volume.

n2185x

I set up a Raspberry Pi 3 with the same distribution, everything updated to the latest. This issue is present on the Pi 3 as well (with lr-atari800).

mitu

@n2185x Then it must be a different issue. Unfortunately the lr-atari800 core hasn't been maintained for a while and hasn't received any bugfixes or improvements that are part of the standalone emulator (atari800).

n2185x

@mitu Is there any particular reason that lr-atari800 hasn't received the bugfixes and improvements that make up the standalone emulator? I would have expected lr-atari800 to be kept in lockstep with atari800.

n2185x

@mitu Since the standalone atari800 emulator is the one that seems to be supported, how can we get it to display through shaders like the ones available for Retroarch? That's really the biggest reason I'm not just using the standalone emulator -- it looks way better with the CRT shader layer.

mitu

@n2185x said in lr-atari800 sound is distorted, while atari800 sound is clean:

@mitu Is there any particular reason that lr-atari800 hasn't received the bugfixes and improvements that make up the standalone emulator? I would have expected lr-atari800 to be kept in lockstep with atari800.

It's up to each upstream project maintainer/developer(s), it may be a technical reason or just lost interest in the libretro fork.

n2185x

@mitu Is there any way we can get the libretro stuff put directly into the atari800 project itself, so that it becomes a first class citizen?

PhoenixFlood

A workaround is to go into the audio settings and turn down the gain to about -5. Clears it right up. I had the same issue.

mitu

@n2185x This can only be decided by the upstream project. While some libretro cores have this setup, it's rather an exception than the rule - the libretro core is generally kept as a separate project.

n2185x

@PhoenixFlood If you're referring to the retroarch audio settings, I tried that and it has no effect on the distortion. The emulator itself doesn't seem to have an audio gain or volume setting.

Shaggy1

@n2185x the distortion I faced with lt-atari800 audio was resolved by applying the patch in this linked thread. The patch, to my knowledge, has not made it into the libretro core

I can confirm that applying this patch and recompiling fixed my audio quality and buzzing

https://retropie.org.uk/forum/topic/22530/lr-atari800-buzzing-sound/4