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. In later models, the DAC is a Burr-Brown PCM55, and vibrato is noticeably faster. 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-98 series of computers. Released in Japan only. Roland RA-50: LA unit with CM-32L ROM (but not all CM-32L samples): Requires software work around or hardware modification to work 100% as a MT-32. Sound quality problems Given the MT-32 was intended to be a relatively low-cost prosumer product, many corners were cut in the design of its DAC output. For example, the circuitry needed to properly calibrate the DACs was omitted, resulting in distortion of the analog signal. Despite having the capabilities of a professional synthesizer module, the noisy output of the MT-32 caused it to be generally considered unsuitable for professional studio use, although it was considered sufficient for use as the sound engine within other Roland prosumer products of the period. For example the E-20 keyboard internally contains a partially unpopulated MT-32 (New) motherboard, while the RA-50 Realtime Arranger uses a highly modified one. However, an aftermarket modification was available from Real World Interfaces to improve the MT-32's sound quality and generally increase its suitability for professional use. Digital overflow The MT-32 and compatible modules use a parallel 16-bit DAC at a sampling rate of 32000 Hz. 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 by shifting all 15 non-sign-carrying data bits to the left, which amounts to multiplying the amplitude by two while keeping the noise floor constant at the analogue output. However, if this doubled amplitude exceeds the amount that can be represented with 16 bits, an arithmetic overflow occurs, audible as a very loud popping or cracking noise that occurs whenever the original signal crosses +16384/-16384 (the value of bit 14 lost in the bit