MIDI & Sound Standards

New to MIDI? This page explains the ideas behind the files PXR plays, along with the sound standards and hardware names you will come across. None of this is essential to enjoy the app, but it helps everything else click into place.

What is MIDI?#

MIDI (Musical Instrument Digital Interface) is a standard from the early 1980s that lets electronic instruments, computers, and software talk to each other.

The key thing to understand: a MIDI file does not contain any recorded audio. Instead it stores a set of instructions, which note to play, how hard, on which instrument, at what moment, along with controls like volume and pan. A synthesizer (either hardware or software) reads those instructions and actually makes the sound.

That has two consequences:

MIDI files are tiny compared to audio files like MP3s.
The same file can sound quite different on different devices, because each synth has its own instruments. This is why the standards below exist, and why PXR lets you choose where the music plays.

What is General MIDI (GM)?#

The General MIDI (GM) logo

General MIDI is the baseline agreement that lets a file play sensibly on any device. It fixes a standard set of 128 instruments in a known order (program 1 is always Acoustic Grand Piano, and so on) and reserves channel 10 for drums. If a file sticks to GM, it will be recognisable on any GM-compatible synth.

What is General MIDI 2 (GM2)?#

The General MIDI 2 (GM2) logo

GM2 extends General MIDI with more instruments and a little more control. It sits between plain GM and the manufacturer standards below, while staying compatible with GM.

What is Roland GS?#

The Roland GS logo

GS is Roland's extension of General MIDI. It adds many more instruments and built-in effects such as reverb and chorus, and was built around Roland's Sound Canvas modules. A GS file can call on those extras for a fuller, more specific sound than plain GM.

What is Yamaha XG?#

The Yamaha XG logo

XG is Yamaha's extension, going further again with very large instrument sets and deep editing of effects and voices. It was built around Yamaha's MU series and later keyboards. Modern XG gear adds thousands more voices on top, and PXR shows an XG MODERN badge when a file uses them: the Genos 2 and Genos arrangers, the Tyros series (Tyros 5, Tyros 4 and earlier), the PSR-SX and PSR-S arrangers, and the Motif, MOXF and MODX workstations.

What are the SC-55, MU80, and the rest? (the hardware)#

These are the classic sound modules the standards grew up around. Many MIDI files were made on or for a specific model, so they sound their best on that exact model (or a faithful software emulation of it).

Roland Sound Canvas (GS): SC-55, SC-88, SC-88 Pro, SC-8850. The SC-55 in particular defined how a whole generation of game and PC music sounds.
Yamaha MU series (XG): MU50, MU80, MU90, MU100, MU128, MU1000, MU2000.

PXR lets you pick which model a file should use and route it to the right device, so a piece written for an SC-55 or an MU80 plays as intended. (Older Roland MT-32 music works differently again, see MT-32 Support.)

The classic modules at a glance#

Manufacturer	Model	Year	Voices	Effects	Polyphony	Channels
Roland	MT-32	1987	128	Reverb	32 partials	9
Roland	SC-55	1991	317	Reverb, chorus	24	16
Roland	SC-55mkII	1993	354	Reverb, chorus	28	16
Roland	SC-88	1994	654	Reverb, chorus, delay, EQ	64	32
Yamaha	MU80	1994	729	Reverb, chorus, variation, EQ	64	32
Yamaha	MU50	1995	737	Reverb, chorus, variation, EQ	32	16
Roland	SC-88 Pro	1996	1,117	Reverb, chorus, delay, EQ, insertion	64	32
Yamaha	MU90	1996	779	Reverb, chorus, variation, insertion, EQ	64	32
Yamaha	MU100	1997	1,267	Reverb, chorus, variation, insertion, EQ	64	32
Yamaha	MU128	1998	1,342	Reverb, chorus, variation, insertion, EQ	128	64
Roland	SC-8820	1999	1,608	Reverb, chorus, delay, EQ, insertion	64	32
Roland	SC-8850	1999	1,640	Reverb, chorus, delay, EQ, insertion	128	64
Yamaha	MU1000	1999	1,396	Reverb, chorus, variation, insertion, EQ	128	64
Yamaha	MU2000	1999	1,396	Reverb, chorus, variation, insertion, EQ	128	64

Voice counts are each model's total addressable tones, drum kits are extra and tallied differently by different sources. Polyphony is the maximum simultaneous notes; the MT-32 is rated in partials, which works out to roughly 8 to 9 voices at once in practice. Channels are the multitimbral parts, which the 32- and 64-part modules spread across more than one MIDI port.

How PXR uses all of this#

It detects GM, GM2, GS, or XG automatically and shows a badge.
It can route each format to the right device, force a specific model's sounds, and decode the GS and XG setup messages into plain language.

To put it into practice, see MIDI Output & Devices for choosing and routing devices, and The Visualiser for the on-screen badges and readouts.

Where to find MIDI files#

PXR plays Standard MIDI Files (.mid, .midi) and karaoke files (.kar). It does not come with a music library, so you bring your own.

A few pointers worth knowing:

Decades of MIDI music exist online, from game and demo soundtracks to pop arrangements and classical pieces. Files made for a particular sound module (a Roland SC-88, say, or a Yamaha MU series) tend to sound their best when played to that module or a close match, which is exactly what PXR's format routing is for.
Karaoke (.kar) files are ordinary MIDI files with the words embedded, so they show synced lyrics.
Keep a file's companion pieces (cover art, an MT-32 setup, a unique SoundFont) in the same folder, and add that folder under MIDI Library Folders so PXR loads them for you.

Some places to start#

These are well-regarded free collections, with plenty for XG fans in particular:

XG-Central is an archive of original XG compositions from composers around the world, free to stream or download, and a fine showcase of what the XG standard can do.
PSR Tutorial keeps a large community song library for Yamaha keyboards, with a strong selection of XG files.
JayB Music offers free original compositions by JayB in General MIDI, General MIDI 2 and XG.

As with any download, only use files you are entitled to, and treat anything from an unfamiliar source with the usual care.