Roland MT-32
LA Synthesis
The name LA
Roland aimed at counterattacking YAMAHA DX7 in creating their first fully-digital synth, D-50.
While DX7 sold quite well and overwhelmed all other synth manufacturers,
it was notorious for its cryptic concept and user interface.
Roland created a new waveform-generation system, but fashioned it like an analog synth/rompler.
They used the name Linear to show its easy operation and predictability.
The actual synthesis engine uses some complex waveform operation,
and LA synths have more interesting - more or less unpredictable - features like Ring Modulation,
in contrast to simple subtractive synths.
The nature of LA's PCM
Roland tells us in the figure that the PCM is processed by DSP's interpolation.
The interpolation function reminds me of Roland's samplers at that time - S series
(S-10, S-50, S-550 and others).
S series adopted "Expanded 16-bit DI - Differential Interpolation."
DI uses 12-bit data and expand them to 16-bit by interpolation.
As S series sounds much better, LA synths' PCM may not be related to DI.
Roland never clarified LA synths' PCM bit resolution.
It may be 12-bit like S series, but I suspect it to be even less.
LA or VA
The synth partial can be seen as a kind of VA - virtual analog.
The only difference is that its often sounds thin and that its filter does not self-oscillate.
But it's not a real VA, as it has no real filter.
If it has the real filter, it could be used with PCM partials as well.
LA just emulates the filter in the waveform generation process (See the figure).
As such, the synth partial belongs to the realm of older analog emulation -
CASIO's PD synthesis,
and even the YAMAHA's FM synthesis,
especially when interpreted as in KORG DS-8's user interface.
I wonder why YAMAHA sued CASIO but not Roland
for analog emulation using sine waves
(see CASIO CTK-1000 page).
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4. 18. 2004