Yamaha MU100R Owner's Manual page 190

Problem
About VL Section Some voices sound
as if they are in the
original octave
even when shifted
down an octave.
Portamento
produces more of a
glissando effect on
some voices.
The filter, EG, and
other parameters
have more effect on
some voices than
others.
Some bowed string
instrument voices
tend to "squeek".
Pitch bends
produced by a
pitch bend wheel
are not always
accurate.
Some voices don't
respond as
expected to EG
edits.
The VL section is a
monophonic tone
generator. Why is
the "poly" mode
initialy selected
when the VL-XG
sound module
mode is engaged?
Possible Cause and Solution
This is because Virtual Acoustic synthesis accurately simulates the acoustic behaviour of
a pipe or string. Simply stated, the harmonic balance of the voice when played in the
normal octave is retained even when the voice is shifted down an octave. The change in
timbre can be greater or less, depending on the selected voice.
Trumpets and some other brass instruments tend to exhibit this phenomenon more than
others. In a VA tone generator portamento is produced by lengthening or shortening the
instrument's pipe or string and changing the Embouchure. A trumpet is designed to em-
phasize the "modes" of the pipe(s) to produce notes over a wide range using only three
valves. When portameto is applied to a trumpet voice, the pitch tends to jump from mode
to mode, thus producing the observed glissando effect. The same effect occurs with some
flute voices. Saxophone modes are not nearly as strong as trumpet modes, but some sax
voices do have two definite modes which, when spanned by a portamento slide, can pro-
duce irregularities.
Most voices use the low-pass filter type, but some use the bandpass, high-pass, or band
eliminate types. Some voices use very little filter processing at all. Changing the filter
settings may not produce a particularly noticeable effect. Also the internal Breath Noise,
Throat Formant, Growl, Harmonic Enhancer and Pitch EG parameter settings can have a
significant effect on how much the parameters accessible via the VL section controls
actually affect the sound.
As anyone who has played (or tried to play) a real violin knows, these instruments natu-
rally tend to squeek if not properly controlled. The same occurs with VA synthesis. As
with a real bowed string instrument, bow speed and pressure must be properly controlled
in the VL section to produce the desired sound. Bow speed is usually controlled either via
breath control or an expression pedal. Bow pressure is controlled via control number 13:
"64" is medium pressure, lower values produced reduced bow pressure, and higher values
produce increased bow pressure.
Natural acoustic musical instruments have no "pitch parameter". Pitch is determined by
the properties of the instrument's resonant body as well as the condition of the instrument's
driver. The same applies to Virtual Acoustic Synthesis: in the VL section's pitch bend is
simulated by manipulating the appropriate pipe/string length and driver characteristics.
As a result, the pitch bend range may not always be "mathematically" accurate.
With reed instruments such as saxophone or clarinet, highly realistic pitch bends are pro-
duced by controlling both pitch and embouchure at the same time. Since the embouchure
component of the pitch bend behaves with characteristics acoustic unpredictability, pre-
cise pitch bends are not always produced.
The effect of editing envelope generator parameters may not always be as expected —
particularly with plucked string instrument voices such as guitar or bass. This is because
the VL section actually simulates the plucking, free oscillation, and muting of the strings
rather than simply using an EG to approximate these events. If the sound of a string voice
decays naturally, for example, setting a long release time will have little or no effect on
the actual sound of the voice. Since the attack and decay portions of the voice also have
natural timbre variations, these can be unnaturally altered by inappropriate EG settings
— which is OK if you're trying to produce an unnatural effect. Trial and experimentation
and the only sure ways to determine how the EG parameters are going to affect a particu-
lar voice.
This is to provide compatibility between the currrent XG format and future polyphonic
VL-series tone generators. It also provides a certain degree of compatibility to allow
playback of VL-XG song data on existing tone generators which do not feature the VL-
XG extension. Specifically, to switch the VL section to the mono mode a "mono mode"
command (control change no.126, value 0-16) is embedded in the song data which, when
received by a 32-note or 64-note polyphonic XG tone generator, switches the appropriate
parts to the mono mode. The same will apply to future polyphonic VL-series tone genera-
tors, so no changes will be required. The VL section therefore has a "poly" which is
automatically selected when a MIDI "XG on" system exclusive message is received.
Appendix
Troubleshooting
179