Chimes/Low volume distortion

Low volume distortion (LVD) is the colloquial term for a hardware bug the YM2612 chip has, in regards to its volume. When quiet sounds are played on the YM2612, unusually high levels of quantization noise cause the output to become corrupted. This manifests as "buzzy" or "pulsy" sounds, especially with pure tones i.e. sine waves. LVD breaks the psychoacoustic volume curve of the sound output, which makes the sound seem like it "holds" in volume as the volume decreases.

The low volume distortion bug was present for much of the Mega Drive's early life, when the system's hardware used discrete YM2612s. Following the year 1993 with the release of the Mega Drive Model 2, low volume distortion was fixed with a new chip revision called the YM3438.

Due to its undocumented nature, awareness of the low volume distortion hardware bug was originally small outside of early internet observations of certain sounds in some video games being more quiet from console to console. There isn't a exact standard to the name of the low volume distortion bug: it's been referred to as the DAC distortion, the TDM artifact, the ladder effect, the volume glitch, etc. For consistency's sake, low volume distortion/LVD is the term being used.

To get around the bug causing improper volume curves with quiet sounds, the low volume distortion bug was used in certain early games like After Burner II and Batman to even out the volume level. This causes certain sounds to become too quiet or uneven in volume on Mega Drive consoles that have the LVD fix. After Burner II's Red Out has a descending pulse that's inaudible in LVD-fixed consoles.

todo: add more here and document instances of LVD, and maybe add sources and examples

Prior to the 2020s very few emulators supported emulation of the low volume distortion errata. The Mega Drive Mini emulates LVD, and the Mega Drive Mini 2 also emulates LVD.

Sonic Origins' Sonic 3 remaster utilizes audio mostly recorded from a older console with the LVD bug, which manifests as certain sound effects lasting for a lot longer like the spring sound and unusual phantom melodies in Angel Island Act 1's music.