From: Ken_Beesley.PARC@XEROX.COM
Newsgroups: rec.music.synth
Subject: MIDI wind instrument
Date: 15 Sep 92 17:03:00 GMT


Brian Good writes:
>the WX7 emits velocity (I *think*;  it's been about
>three years since I used one extensively), while the EWI emits a constant
>(though user-selectable) velocity


Looking at my WX7's output, in a MAX program, I found that it does indeed
include a meaningful value in the velocity byte of each NOTE-ON message.  It
seems to be just a copy of the Breath Control value at the moment that the
NOTE-ON is generated.

On the WX7, a sensor periodically measures how hard you are blowing and
digitizes the information into a number from 0-127.  These numbers can be
transmitted in MIDI messages labeled either as Breath Control or Aftertouch,
depending on the setting of a dip switch.  In addition, the same information
(how hard you are blowing) can be redundantly transmitted as MIDI Volume as
well (controlled by another dip switch).  This flexibility was built in to
allow compatibility with a range of synthesizers and drum machines, which are
often severely limited in the kinds of MIDI messages they can recognize and
respond to.  I believe that the newer WX11 is less flexible in the kinds of
MIDI messages it can transmit (other useful features were engineered out as
well).

If indeed the EWI fails to transmit meaningful velocities, you could simulate
WX behavior via a MAX program.  Simply intercept all NOTE-ON messages, grab the
current Breath Control value, and substitute that value in the velocity byte
before sending the NOTE-ON message on its way.  Such a program would be
trivial.  This should allow the EWI to control percussive, bass and piano-like
patches, where velocity (along with an envelope generator) is the key parameter
that controls volume.

For wind-instrument-like patches, velocity makes little sense as a volume
control.  The key to writing wind-instrument-like patches is to control the
volume of the patch with Breath Control (or whatever is being transmitted in
response to how hard you are blowing).  I.e. don't control the volume with
velocity and an envelope generator as in a piano-like patch.  In wind patches,
it would be nice if the velocity information, transmitted only once for each
NOTE-ON, could be something other than just a copy of the Breath Control value
at the time of the NOTE-ON.  For example, with suitable sensors, the velocity
value could be an indication of how hard the player tongued the note.  Then
that velocity information could be used to control the breathy "chiff" that
starts a tongued note.

>On the other hand, the EWI (which is hard-wired to its analog module) is a
>bit more expressive than any pure-MIDI device I know.  I've also used mine to
> drive a Wavestation A/D with generally good results.

The EWI continuously senses how hard you are blowing and converts that into a
continuous control voltage that is hard-wired to the amplifiers in its
dedicated analog synth.  It is not surprising that such a scheme allows very
smooth and subtle control of volume.  The WX7, on the other hand, is limited to
sending digitized Breath Control (or Aftertouch, and optionally MIDI Volume)
values ranging from 0 (no blowing pressure, or pressure below a cute-off
threshold) to 127 (maximum volume).  Even under the best circumstances, having
only 127 discrete volume steps can result in discernably ragged crescendos and
decrescendos.  On top of that, the WX7 can't send Breath Control
continuously--it has to sample the pressure periodically (the Sample Rate) and
send discrete Breath Control messages at little intervals.

Unfortunately, the sample rate on the WX7 seems a little slow.  Looking at the
actual BC values being transmitted during a crescendo (again, in a MAX
program), it is not unusual to find a string of values like  54 55 57 60 63 65
68.  That is, presumably the actual breath pressure during the crescendo could
be digitized as a string of continuous values  54 55 56 57 58 etc., but the
slow sample rate is catching and transmitting only every second or third value.
This obviously makes crescendos even more ragged.

When the EWI's analog synth converts the control voltage information into MIDI
to send out to a MIDI synth, it too is limited to sending Breath Control values
from 0 to 127.  So an EWI controlling a MIDI synth like the Wavestation A/D or
the Yamaha TG77 cannot, ideally, be any more expressive in controlling volume
than a WX7.  However, if the EWI samples and transmits Breath Control at a
higher sample rate, or if its breath pressure sensor is more responsive, then
the overall volume control could be more expressive.  I would love to see what
the MIDI output of the EWI really looks like.

Ken Beesley
beesley.parc@xerox.com