Roland MT-32

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The Roland MT-32 is a MIDI - synthesizer module, the first time in 1987 by the company Roland was sold.

Roland MT-32

Performance characteristics

As with the Roland D-50 , the MT-32 ( M ulti- T imbre) uses linear arithmetic synthesis, a form of sample- based synthesis combined with subtractive synthesis , to generate sound. Samples are used for drums and for the attack phase, while the sustain phase is generated in the traditional way.

The MT-32 contains a library of 128 synthesizer and 30 rhythm sounds, which can be played on eight melodic and one rhythm channels. It also has a digital reverb effect. Successor models (see below) expand the sound library by 33 sound effects. Since no piano attack sample is available, the MT-32 cannot produce a convincing piano sound.

As a full-fledged synthesizer, the MT-32 is very programmable, in contrast to simple wavetable devices. A sound consists of four partials , which can be combined in different ways (including ring modulation ). A total of 32 Partials are available, whereby the polyphony depends on the tonal complexity of the music, so that between 8 and 32 notes can sound simultaneously.

By default, the MT-32 does not play on the otherwise popular MIDI channel 1 (and consequently neither does MIDI files written for the MT-32), but it can be reprogrammed to do so, for example by a certain degree of General -MIDI compatibility to achieve.

Models

The MT-32 technology can be divided into three generations:

First generation

MT-32 internal structure

The first generation does not have a headphone jack. LA32 sound generation chip is an 80-legged pin grid array . Control CPU is an Intel 8095 . The digital-to-analog converter is a Burr-Brown PCM54 without an optional setting potentiometer; its input signal has a resolution of 15 bits (see below).

  • MT-32 with PCB revision 0, used in devices up to serial number 851399.

The PGA-LA32 chip will later be replaced by a flat 100-leg type.

  • MT-32 with "old" board revision 1, used in devices with serial numbers 851400 to 950499.
  • Roland MT-100 : A combination of the MT-32 with the Roland PR-100 hardware sequencer.

Second generation

A headphone jack is added. Control CPU is an Intel 8098 . Same digital-to-analog converter, but the input signal has a resolution of 16 bits (see below).

  • MT-32 with "new" board revision 1, used in devices from serial number 950500.

After that, all compatible modules have 33 additional sound effect samples.

  • Roland CM-32L : Sound module for use with a computer ("CM-" stands for "Computer Music"); only has a volume control, a MIDI message and a power indicator lamp as external control elements. Published 1989.
  • Roland CM-64 : A combination of the CM-32L with the sample-based Roland CM-32P , the "Computer Music" version of the Roland U-110 . The CM-32P part plays on the MIDI channels that are not used by the CM-32L part.
  • Roland LAPC-I : ISA bus expansion card for IBM PCs and compatibles. Contains the MPU-401 interface.
  • Roland RA-50 : Automatic accompaniment with integrated MT-32 sound generator (ROM module of the CM-32L).

Third generation

The digital-to-analog converter is now a Burr-Brown PCM55, which is factory set (see below). The vibrato is noticeably stronger than in previous models.

Sound quality and compatibility issues

Clipping

The MT-32 and all compatible modules use a parallel 16-bit digital-to-analog converter with a sampling rate of 32 kHz. In order to improve the signal-to-noise ratio without investing in higher quality components, the amplitude of the digital input signal is doubled:

  • in modules of the first generation by omitting bit 14 (the most significant bit) and shifting the remaining bits to the left, which reduces the effective resolution to 15 bits;
  • in later modules by the fact that the LA32 sound generation chip itself generates digital waveforms of higher amplitude.

In both cases, this creates a loud distortion noise when sounds are played at very high volume.

Differential linearity error

The digital-to-analog converter used in first and second generation modules , a Burr-Brown PCM54, requires an external adjustment potentiometer (although supposedly factory-adjusted) to correct for the differential linearity error.

For reasons of cost, Roland did not install such a circuit; for this reason, soft tones have a slightly metallic sound. This distortion is much more pronounced on the first generation MT-32, possibly because bit 0 is not connected due to the bit shift (see above); however, the effect can also be heard to a lesser extent on models of the second generation.

In third-generation modules, Roland instead used the factory-adjusted Burr-Brown PCM55, which has almost no audible linearity error.

Buffer overflows

First generation devices with firmware versions below 2.00 require a delay of 40 milliseconds between two system exclusive messages. Some computer games that have been programmed for compatible or later control ROM versions will not work with such early devices and produce incorrect sounds or cause the firmware to crash.

Music for PC games

The MT-32 was used extensively in PC games of the late 1980s and early 1990s as a high quality alternative to AdLib and SoundBlaster cards for creating music and sound effects. Sierra On-Line was the first to support him in their 1988 game King's Quest IV; they also sold the module.

With the increasing popularity of the General MIDI standard and its reference implementation in the Roland Sound Canvas modules, support for the MT-32 dwindled in 1993 in favor of the General MIDI standard, which was used by many wavetable- based sound cards. Instead of using their own sounds and music data specially optimized for the MT-32, later games simply reprogrammed the sound library of the MT-32 so that it roughly corresponded to the General MIDI Level 1 specification, provided the MT-32 was still supported .

emulation

Because of the popularity of the MT-32 for playing music from PC games, many modern sound cards offer a simple "MT-32 emulation mode", usually implemented either by a SoundFont consisting of General MIDI instruments, which are arranged according to the standard MT-32 sound sequence , or by recording the original MT-32 sound. The result is often perceived as poor because the sampling technology cannot reproduce the pitch and time-varying characteristics of the original synthesizer technology; programming your own sounds (see above) is also not supported at all.

More recently, attempts have been made to emulate LA technology in software using the original PCM and control ROMs. The open source project Munt, which tries to emulate the MT-32 hardware using a WDM driver for Windows XP , is significant; it is also part of ScummVM . Munt is based on the earlier MT-32 Emulation Project, which was the reason for a brief legal dispute with Roland, the manufacturer of the MT-32, about the distribution rights of the original ROMs.

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