Roland MT-32
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The Roland MT-32 Multi-Timbre Sound Module is a MIDI synthesizer module first released in 1987 by Roland Corporation. Along with its compatible modules, it established an early de-facto standard in computer music and was the first product in Roland's ミュージくん line of Desktop Music System (DTM) packages in Japan.
Within Roland's family of LA synthesizers, the multitimbral MT-32 series constitutes the budget prosumer line for computer music at home, the multitimbral D-10/D-20/D-110 models the professional line for general studio use, and the high-end monotimbral D-50/D-550 models for sophisticated multi-track studio work.
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[edit] Features
Like the Roland D-50 Linear Synthesizer, it uses Linear Arithmetic synthesis, a form of sample-based synthesis combined with subtractive synthesis, to produce its sounds. Samples are used for attacks and drums, while traditional synthesis assures the sustain phase of the sounds.
The original MT-32 comes with a preset library of 128 synth and 30 rhythm sounds, playable on 8 melodic channels and one rhythm channel. It also features a digital reverberation effect. Successors (see below) added a library of 33 sound effects. Because of the absence of a piano attack sample, it cannot play a convincing acoustic piano sound.
Being a synthesizer rather than a simple wavetable device, the MT-32 is very programmable. Sounds are created from up to 4 partials which can be combined in various ways (including ring modulation). With 32 partials available overall, polyphony depends on the tonal complexity of the music, and 8 to 32 notes can be played simultaneously.
The MT-32 by default does not play on the otherwise most popular MIDI channel 1 (and by consequence neither do MIDI files targeted for it), but can be reprogrammed to do this, through MIDI system exclusive messages, for example to achieve a certain level of General MIDI compatilibity.
[edit] Models
Three major versions of the MT-32 technology can be isolated:
[edit] First generation
No headphone jack. LA32 sound generation chip is an 80-pin PGA. Control CPU is an Intel C8095-90. DAC is a Burr-Brown PCM54 without trimpot; its input signal has a resolution of 15 bits (see below).
- MT-32 with revision 0 PCB, used in units up to serial number 851399.
The PGA LA32 chip is later replaced with a 100-pin flat type.
- MT-32 with "old-type" revision 1 PCB, used in units with serial numbers 851400 - 950499.
- Roland MT-100: A combination of the MT-32 with the Roland PR-100 hardware sequencer.
[edit] Second generation
A headphone jack is added. Control CPU is an Intel P8098. Same DAC, but with full 16 bits of input signal resolution (see below).
- MT-32 with "new-type" revision 1 PCB, used in units with serial numbers 950500 and up.
After this, all compatible modules feature 33 additional sound effect samples.
- Roland CM-32L: Sound module for use with a computer ("CM-" stands for "computer music"), having only a volume knob, a MIDI message and a power-on indicator as external controls. Released in 1989.
- Roland CM-64: A combination of the CM-32L with the sample-based CM-32P, a cut-down "computer music" version of the Roland U-110. The CM-32P part plays on MIDI channels 11-16 which are not used by the CM-32L part.
- Roland LAPC-I: ISA bus expansion card for IBM PCs and compatibles. Includes the MPU-401 interface.
[edit] Third generation
DAC is now a Burr-Brown PCM55, which is factory-trimmed (see below). Vibrato is noticeably faster than on previous models.
- Roland CM-32LN: Sound module for the NEC PC-98 series notebook computers, featuring a special connector for direct connection to the computer's 110-pin expansion port. Released in Japan only.
- Roland CM-500: A combination of the CM-32LN with the Roland GS-compatible Roland CM-300, the "computer music" version of the Roland SC-55. Released around 1992.
- Roland LAPC-N: C-Bus expansion card for the NEC PC-88 and NEC PC-98 series of computers. Released in Japan only.
[edit] Sound quality and compatibility problems
[edit] Clipping
The MT-32 and compatible modules use a parallel 16-bit DAC at a sampling rate of 32 kHz. In order to improve the signal-to-noise ratio without investing in higher-quality components, the volume of the digital signal fed into the DAC is doubled:
- in first generation modules by dropping bit 14 (the highest monotonic bit) and shifting the remaining bits to the left, reducing the effective resolution to 15 bits.
- in later modules by having the LA32 synthesizer chip itself output digital waveforms with a higher amplitude.
In both cases, this results in a very harsh clipping noise when playing sounds at a high volume.
[edit] Differential Non-Linearity Error
The DAC used in first- and second-generation modules, the Burr-Brown PCM54, although purportedly factory-trimmed, requires an external trimpot to reduce the Differential Non-Linearity Error (DNL).
To save on cost, Roland did not provide such a circuit, causing low-volume signals to have a noticeable metallic or "grungy" sound. This distortion is far more pronounced on the original MT-32, possibly because the DAC's bit 0 is completely unconnected due to the bit shift (see above), but is slightly audible on the new-type MT-32 and the CM-32L as well.
For third-generation modules, Roland used the Burr-Brown PCM55 DAC instead, which is factory-trimmed and thus has almost no audible Differential Non-Linearity error.
[edit] Buffer overflows
First generation units, having control ROM versions below 2.00, require a 40 millisecond delay between system exclusive messages. Some computer games which were programmed to work with the compatible modules (see above) or later ROM versions that do not require this delay, fail to work with these units, producing incorrect sounds or causing the unit to lock up completely.
[edit] Music for PC games
The MT-32 was used extensively in PC computer games of the late 1980s and early 1990s as a high-end alternative to AdLib or Sound Blaster sound cards for producing game music and sound effects. Sierra On-Line was the first company to support it in their 1988 game King's Quest IV; they also sold the module.
With the popularization of the General MIDI standard and its reference implementation in the Roland Sound Canvas, starting in 1993, support for the MT-32 waned in favor of the General MIDI standard used by many wavetable-based sound cards. Instead of providing custom sounds and music data specifically optimized for the MT-32, later games would simply program the MT-32's sound bank to roughly match the General MIDI Level 1 specification, if they supported the MT-32 at all.
See also: List of MT-32-compatible computer games
[edit] Emulation
Due to the popularity of the MT-32 as a music playback device for PC games, many modern sound cards provide a simple "MT-32 emulation mode", usually realized by way of a sound font comprised either of General MIDI instruments rearranged to roughly represent the MT-32's preset sound bank, or of samples directly recorded from the original unit. Results are often considered poor, as the sampling technology used can not reflect the pitch- and time-variable characteristics of the original synthesizer technology, with the programming of custom sounds (see above) not being supported at all. One exception is the Orchid SoundWave 32 card released by Orchid in 1994, whose on-board DSP allowed for a more faithful reproduction of the original sound characteristics.[citation needed]
More recently, there have been attempts at emulating the LA synthesizer technology in software using images of the original PCM and control ROMs. The most notable of these emulators is the Open Source project, Munt, which currently tries to emulate the MT-32 hardware by way of a WDM driver for Windows XP. It is also incorporated into ScummVM, an Open Source Lucasarts adventure game interpreter, as of version 0.7.0. Munt is based on an earlier MT-32 Emulation Project, which was the source of a short-lived legal squabble over distribution of the original ROM images with Roland Corporation, who manufactured the MT-32 and claims copyright on the ROM's data.
Roland has recently been offering its own emulation of classic synthesizers, notably of the D-50.
