HPAVC/HPAVC CD-ROM.iso/pc/IT212.ZIP/MIDI.TXT

Text File | 1997-04-22 | 16.6 KB | 390 lines

-------------------------------------
## Impulse Tracker MIDI Supplement ##
-------------------------------------

Introduction
============

The biggest new addition to Impulse Tracker 2.12 has been support for
sending data out through the MIDI protocol. Earlier versions of Impulse
Tracker (IT) have had support for incoming MIDI data, so it was possible to
play on a 'MIDIfied' keyboard and have IT 'track' all the notes down in the
pattern in realtime.

MIDI out, however, is a completely different ballgame. You in fact don't
have to read this supplement at all if you wish to get MIDI working, but in
order to gain full usage of MIDI out, you will have to read this in order
to understand how IT's MIDI support fully works


MIDI Support & Soundcards
=========================

At present, the only sound devices IT supports for MIDI output are the AMD
InterWave and the Creative Labs Sound Blaster AWE32. No planned support has
been done for other sound devices. Do NOT bug Pulse to add MIDI out support
for your soundcard, your mail will simply be deleted.


Enabling MIDI
=============

To enable MIDI output, you must first have IT on Instrument control mode
rather than Sample control mode. To do this, press F12 to go to the Song
Variables screen and switch control to 'Instruments' if you haven't already
done so.

MIDI & Instruments
==================

MIDI Channel
------------

New to the Pitch section of the Instrument screen (press F4 and select the
"Pitch" button) are the sliders "MIDI Channel", "MIDI Program" and "MIDI
Bank". Once the MIDI Channel value for that instrument is set to a value
other than zero, IT will send out MIDI data whenever that instrument is
encountered in a pattern, on that particular MIDI Channel. What data IT
actually sends through the MIDI port will be a note on command, although
this will be discussed in more detail later.

MIDI Program/MIDI Bank
----------------------

The MIDI Program and MIDI Bank sliders work in a similar manner to each
other. If they have a value set to -1, IT will not transmit a program change
message nor a bank change message for that instrument. If you specifically
set a MIDI Program for that instrument, IT will send a 'program change'
message along with the 'note on' message.

The MIDI Bank instrument setting is also the same; IT will not send a bank
change message if the MIDI Bank slider is set to Off (ie: has a value of
-01). If the MIDI Bank setting is active for that instrument, IT will send
it along with the note on message as well.

Summary
-------

IT will always send a 'note on' command for a particular MIDI channel
whenever a MIDI instrument is encountered in the pattern. (A MIDI instrument
is simply an instrument where the MIDI Channel value has been set to
something other than 0). IT will also send a program change command and/or a
bank change command along with the note on command if they are set active.


More Advanced MIDI
==================

How MIDI Works
--------------

MIDI is not a file format (like IT is a module format) nor is it even a file
layout. MIDI is a computer protocol (or language) which is used to
communicate between devices . You may like to think of it as a network,
where the MIDI cables are the cables yo u lay between computers, and MIDI is
the network protocol (such as Novell NetWare, Windows Networking or TCP/IP)
used to communicate between the sound devices. When an instrument is said to
be 'MIDI compliant', that means that it has support for the MIDI protocol
and understands MIDI messages.

The .MID file format is simply a way to store these messages. It is a
collection of MIDI data, and when a .MID file is run through a MIDI player,
all the MIDI player does is send the data in the .MID file out through the
computer's MIDI port. In a network analogy, if you can imagine that every
single transaction run through the network was being logged to a file on
your hard disk; that every single byte was being recorded to a logfile, this
is what a .MID file is.

An example of MIDI Communication in IT
--------------------------------------

You've read above that when IT encounters a MIDI instrument in the
patterndata, it sends a 'note on' command, which is defined in the MIDI
protocol to be 'Play this note on this MIDI channel at this particular
velocity'. (Velocity is similar to volume ). If you play a MIDI instrument
which is mapped to MIDI channel 2 at C-5 with a velocity of 64, the actual
data which IT sends out to the MIDI port resembles something like this (in
hex):

    Note On with parameters;
        MIDI Channel: 2
        Note: C-5
        Velocity: 64

        Data that IT sends out (hex): 91 3C 40
        Data that IT sends out (decimal): 145 60 64

We'll run through each of these three bytes step by step.

The first byte (91 in hex, or 91h) is the actual 'Note on' command. It tells
the receiving MIDI device that the data which follows is part of the 'note
on' data. An analogy which trackers may find useful is the effect column.
There, you have an effect command and effect data; for example, the effect
'G20' can be split up into two parts--'G' and '20'. The 'G' part is the
actual effect command which tells IT that you wish to perform a portamento,
and the '20' part is the effect data, or in this case the spe ed at which
the portamento should occur. In this MIDI example, the '9' is the MIDI
command and the '1 3C 40' is the rest of the data for that command.

Now, the second digit (1 in our example) specifies the MIDI channel. MIDI
channels are 0-based; that is, if you want to send to MIDI channel 6, IT
specifies 05 for the actual data. MIDI channel 10 is 09h, MIDI channel 14 is
0Dh, etc. Here we're sending t o MIDI channel 2, so the value sent out over
MIDI is 01h.

The first byte (91 in hex, or 91h) is the actual 'Note on' command. It tells
the receiving MIDI device that the data which follows is part of the 'note
on' data. An analogy which trackers may find useful is the effect column.
There, you have an effect com mand and effect data; for example, the effect
'G20' can be split up into two parts--'G' and '20'. The 'G' part is the
actual effect command which tells IT that you wish to perform a portamento,
and the '20' part is the effect data, or in this case the spe ed at which
the portamento should occur. In this MIDI example, the '9' is the MIDI
command and the '1 3C 40' is the rest of the data for that command.

Now, the second digit ('1' in our example) specifies the MIDI channel. MIDI
channels are 0-based; that is, if you want to send to MIDI channel 6, IT
specifies 05 for the actual data. MIDI channel 10 is 09h, MIDI channel 14 is
0Dh, etc. Here we're sending t o MIDI channel 2, so the value sent out over
MIDI is 01h.

The second byte (3Ch) is actually the note to send (C-5 here). In MIDI, all
command (parameter) data is between a scale of 00h-7Fh (or 0-127 in
decimal). Notes are transmitted the same way - via numbers. If you imagine
C-1 is sent with a value of 00h, C#1 i s 01h, D-2 is 02h, etc, then the note
we want to play, C-5, has a value of 3Ch (60 decimal).

Now the first and second bytes are done with, the fourth byte should be
fairly easy to understand. This byte represents the velocity at which the
note should be played. In our case, we want a velocity of 64, which
translates to 40h, and so this is the value which is sent out.

So to recap, we have three bytes for the note on command, "91 3C 40".

        Byte 1: 91 == Note on command (on MIDI channel #2)
        Byte 2: 3C == Note on data (Note to play, C-5)
        Byte 3: 40 == Note on data (Velocity of 64 decimal)

Configuring IT's MIDI out data
------------------------------

Keeping the above example in mind, press Shift-F1 to get to IT's MIDI screen
and press the 'MIDI Output Configuration' button. This will take you to IT's
MIDI out engine. Now, if you examine the 'Note On' field, it reads:

    9c n v

This can be correlated to our above example of '91 3C 40'. Now, the 'c n v'
in the Note On field corresponds to 'channel', 'note' and 'velocity'. Think
of them as variables; IT will substitute the appropriate channel, note and
velocity values which it encounters in the MIDI instrument information
and/or patterndata.

If you now actually defined a MIDI instrument to play on MIDI channel 2, and
you played it in a pattern at C-5 with velocity 64, all IT does is read the
'Note On' field from the MIDI configuration screen and substitute '1' for
'c', '3C' (C-5) for 'n' and '64' for 'v'. Therefore, IT will read '9c n v'
and replace it with '91 3C 40'.

In any of the MIDI output fields, lowercase letters represent variables (or
subsitutions which IT should make) and uppercase letters or numbers are
constants which IT writes to the MIDI port directly without any change.
Therefore, these fields are case se nsitive--for the note on command, '9c n
v' is blatantly different to '9C n v'. 9c represents 'send byte 09 followed
by the MIDI channel byte', whereas 9C represents 'send the byte 9C'.

In short, 0-9 and A-F are treated as hexadecimal constants and will be
passed through directly. Lowercase letters will be treated as variables and
substituted accordingly. Note that variables are regarded as 'full bytes' by
themselves and are never part of an actual byte sequence except for the
variable 'c', so '9n' is exactly the same as '09 n' or '9 n'; all of them
will expand to the sequence '09 <MIDI note byte>'. 'c' is the only value
that takes on a nibble (4-byte) value, due to the MIDI protocol definition.
This means that 9c will actually become one byte when expanded, with the
lower digit representing the channel.

IT MIDI Variables
-----------------

c: MIDI channel

        This is simply the MIDI channel of which the instrument is set
to, 0-based. Note that this is the only nibble sized variable.

n: note value

    A value from 00-7Fh representing the note to be played, where
C-5 is 60h.

v: velocity

    The MIDI velocity of the note.

u: volume

    Volume is similar to velocity, except that velocity does not
take the volume envelope and fadeout values into account, whereas the
'u' volume variable does.

x: pan set

        Sends a MIDI panning value. This does not take into account
panning envelopes.

y: calculated pan

        Sends a MIDI panning value which does take into account
panning envelopes.

a: high byte of bank select
b: low byte of bank select

    These commands are only really useful in the bank change
field.

z: macro data

    (See section on macros for full explanation).

Configuring MIDI Output for Your Keyboard
-----------------------------------------

In the basic IT distribution, the only fields which have any data are 'Note
on', 'Note Off' and 'Program Change'. The reason for this is that these are
the only commands which are set as standards by MIDI. MIDI commands such as
Change Pan, Bank Select , e tc all differ from synth to synth. There's not
much which can be done to solve this, you will have to look up your synth's
manual to find out the exact MIDI commands it needs to issue a panning
change, bank select, etc.

Some values which you may wish to try, however, will be:

    Change pan: Bc 0A x
    Bank select: Bc 0 a 20 b

These may or may not work. If they do, then great, but if they don't, you
will have to actually RTFM *gasp* in order to get these other commands
working.


Effect Commands & Macros
========================

Now that IT's MIDI engine is understood and the basis of MIDI communication
has been laid down, perhaps the most powerful function of IT's MIDI engine,
macros, will be explained.

Standard Effects
----------------

Firstly, at the moment there is NO support for standard IT effect commands
(such as pitch slide, portamento, vibrato etc) to work via MIDI. This may or
may not be implemented in future. Currently, however, if you perform an E01
effect on a note, nothing w ill happen as far as the MIDI aspect of the
instrument is concerned.

Macro Effects - SFx
-------------------

The SFx command, previously used in the .MOD format as "FunkRepeat", has
been changed in IT to allow for the functioning of MIDI macros. The unused
Zxx command will also now play a part in MIDI functioning.

To understand how this works, it's best to take an example into account. At
the beginning of this supplement, the MIDI sequence '91 3C 40' was used
which was a Note On, MIDI channel #2 played at C-5 with a velocity of 64.
This was represented in IT's MIDI configuration as '9c n v', so it made the
appropriate substitutions to '91 3C 40'.

The Macro Setup section of IT's MIDI Output Configuration screen can be used
to define your own custom MIDI command/data sequences. These can be
absolutely anything you like, from a MIDI SysEx command to a Note On
command. In fact, to start off, we'll tak e a Note On sequence as an example
and we will attempt to emulate the same '91 3C 40' bytes, except that we'll
make this sequence ourselves rather than letting IT do the work for us.

How SFx and Zxx commands relate
-------------------------------

Firstly, remember that IT substitutes values when it encounters variables.
If you glance at the above section on IT MIDI Variables, you'll notice that
the 'z' variable represents macro data. Now that this '91 3C 40' sequence
has been driven into our he ads, try setting the SF0 macro field on IT's
MIDI Output Configuration screen to '91 3C z'.

Remember that the fourth byte in the MIDI sequence (40 in our normal
example) is the velocity to send with the Note On message. The SF0 macro
field you've just defined means that IT will read any Zxx effects and
replace the 'z' variable in the SF0 macro w ith the 'xx' value from the Zxx
effect. To enable the macro, simply put in a SF0 along with a Note On in the
pattern data. Now, all values from Z00 to Z7F will substitute for 'z'
accordingly. So, to show that our SF0 sequence will reproduce the exact same
thing as our Note On command:

    C-5 01 SF0 (this will play the note on command as usual, and
                specify that the SF0 macro sequence should be
                hooked to Zxx effects).
    ... .. ...
    ... .. ...
    ... .. ...
    ... .. Z40 (this will trigger our SF0 sequence with a 'z'
                value of 40h).

The above patterndata should produce a note on event at row 0 in the
pattern, and again at row 4. Now, try replacing the Z40 effect with Z7F and
IT will substitute 'z' with '7F', or a velocity of 7Fh (127 decimal) in our
SF0 sequence. The result should be that you'll hear a Note On with velocity
64 on row 0, and a Note On with velocity 127 on row 4; ie: the second note
triggered will be twice as loud. The The sequence that IT will send will be
'91 3C 7F'.

SFx commands summary
--------------------

Our example above of using a 'note on' command sequence for an SFx effect is
rather pointless, since IT does this effect itself. However, it has
hopefully served its purpose by demonstrating how effects work.

The SFx commands, as you can see, can be redefined to absolutely any MIDI
data at all. This can be something simple like a pitch slide, a complex
SysEx 'set filter to aftertouch' command, or whatever you like. The
possibilities are endless and are only li mited by what your synth can do;
IT's SFx/Zxx combination is customisable enough to handle nearly any MIDI
data you wish to output.

If you wish to take advantage of these commands, you will have to look up
the manual for your synth and get stuck into the MIDI/SysEx section. Please
do not come to any IT support people asking for help on this subject because
every synth is different.

Z80 -> ZFF commands
-------------------

The Z80 to ZFF commands are also macro sequences, but they have no 'z'
variable to substitute for. They are not 'hooked' to any SFx effects, they
are straight, direct macro sequences. For example, if you have a MIDI
controllable effects unit (such as an Alesis MidiVerb), you may wish to
assign the Z80 command to set a up a certain value for the reverb delay
length. Later in the song, you can issue a Z81 command to change the reverb
delay or turn it off altogether.

To summarise, the Z80 to ZFF commands are similar to SFx macro sequences,
but they do not have any extra parameters (whereas the SFx macro's 'z'
variables are controlled by Z00 to Z7F).


Contact Information
===================

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