Emu XL-7 & MP-7 User's Group

On 12/10/02 10:04 AM, "pocketd@..." <pocketd@...> wrote:

> Hi,
> 
> what a great idea to use a controller as pitch source, I`ll check that
> out...
> I read something of an amount of +38 routed to Pitch in the patchcords, but
> how many 
> semitones are that?
> I think the worst thing about XX-7 are the manuals.
> Thanx, again drk....
> 
> Christoph

The +38 was a side of the page comment made in the manual about what the
various LFO pattern waveforms do when modulating pitch.  As I have
experimented with the XX-7 modulation it appears that with a full range
control signal (like a MIDI controller all the way up to 127) a modulation
amount of +38 will produce an octave change in pitch.

The +38 factor is somewhat a puzzling choice (any one from Emu care to
elaborate on this) because it precludes an easy way of getting all of the
useful music intervals since it is not divisible evenly by 12.

It seems that the full scale change in pitch you can achieve by modulating
the Pitch destination with full amount is a bit over two octaves and a 5th.
If you set the Pitch modulation amount to +99 I think it will produce
exactly two octaves and a 5th (31 semitones) when a MIDI controller
producing a full value of 127 is input (which I think the XL-7 equates to a
full-scale internal control signal).

Here's what I think is going on based on some tests.  The pitch range
internally for the XX-7 is 0-127 semitones, which is also the MIDI range.
Emu has chosen the scaling factor of the Pitch modulation to be 1/4 of that
range.  So a full level input modulating Pitch with an amount=100 will
produce a change of 1/4 that range.  Unfortunately 127/4 is not an whole
number.

The range is 127*100/4 cents (one cent = 1/100 of a semitone).  so if you
assign a midi controller to Pitch, or use Key as the modulation source you
will find that each value increment is 1/4 a semitone, 25 cents.  Stated
another way MIDI controlling pitch uses an equal-tempered scale of 48 tones
per octave. 

Here are some handy facts (if I understand this correctly)

When using a clock like the Clock Divisors; the logic modulations sources
like the FlipFlop or the Switch; or a MIDI source at full value = 127 then
the following scale factors are useful to remember:
    1. each increment of modulation amount is about 31.75 cents.
    2. an interval of a 4th is right at a modulation amount of 16 (its a bit
sharp)
    3. an interval of a 6 semitones is a modulation amount of 19
    4. an interval of a 4th is right at a modulation amount of 22
    4. an interval of one octave (12 semitones) is a modulation amount of 38

    other intervals can be calculated by solving interval*100/31.75

The Gain4X is handy if you want to have MIDI values cover the whole pitch
range.

You can do a lot with this beyond controlling pitch with clocks or MIDI
controllers.  You can if your clever have different pitch scales for each
layer in a preset, or at least each preset.  You can also do things like
invert the keyboard for that authentic Josef Zawinul ARP2600 playing style
:-)


drk

www.delora.com/music
www.mp3.com/zdrk
drk.iuma.com