Radio Shack FX2 User Manual download pdf (Page 18)

Ensoniq VFX-SD and SD-1

S e q u e n c e r F i l e F o r m a t s

Part II

Gary Giebler

This month we continue and conclude my description of

VFX-sd and SD-1 sequencer ﬁle formats which was started in

Issue #77.

problem unless you are using extremely large MIDI drum sets

or controlling external devices such as lighting controllers,

MIDI mixers, etc.

V F X - S D a n d S D - 1 T r a c k D a t a F o r m a t

A track consists of a long word (4 bytes) containing the size or

length of the track followed by a stream of sequencer events.

Each Track should start with a clock event to initialize the track

coimter which starts at 01.01.00 (one tick before the start of bar

1). The last track event must be the End of Track event.

T r a c k L e n g t h T r a c k E v e n t s E n d o f T r a c k

00 00 00 00 80 E6 00 01 ... ... 80 E9

VFX-SD and SD-1 Sequencer Events

All of the sequencer events for the VFX-SD and the SD-1 con

tain an even number of bytes. This was probably done because

both keyboards contain 16-bit microprocessors which read and

write data more efﬁciently 16 bits (2 bytes) at a time. When

referring to 16 bits of data, we (in the computer world) refer to

the data as one word. All sequencer events have the most sig

niﬁcant bit (MSB) of the ﬁrst word set to indicate the start of

an event. All subsequent words have the MSB cleared. This al

lows the microprocessor (or us) to skip unknown events or to

move backwards in the track data — something which would

be nearly impossible without marking the ﬁrst word of an

event. Most sequencer events consist of two words (four bytes)

of data. One exception is the End of Track Event which con

tains one word (two bytes).

FIRST EVENT WORD

MSB

Bit: 15 14 13 12 11 10 09 08

Value: 1 d6 d5 d4 d3 d2 dl dO

LSB

07 06 05 04 03 02 01 00

t7 t6 t5 t4 t3 t2 tl to

The least signiﬁcant byte (lower 8 bits t7..t0) of the ﬁrst word

of each event contains the event type, giving us a total of 256

possible event types. The remainder of the ﬁrst word (seven

bits d6...d0 — remember the MSB is always set) contains the

number of clock ticks to delay before executing the next event.

Since the maximum delay is only 127 clock ticks, an event type

(E6 hex) was created to allow longer delays.

KEY EVENTS 00 - 87 (00 - 57 hex)

The ﬁrst 88 event types (00 - 87) (OOh - 57h) refer to the 88

keys (AO - C8) on a piano. Notice that by restricting the se

quencer to 88 key events, the keyboards can't record the full

MIDI note range. Realistically, this probably won't be a

MSB

Word 1: 1 d6 d5 d4 d3 d2 dl dO

Word 2: 0 v4 v3 v2 vl vO n9 n8

LSB

t7 t6 t5 t4 t3 t2 tl to

n7 n6 n5 n4 n3 n2 nl nO

( Word 3: 0 cE cD cC cB cA c9 c8 c7 c6 c5 c4 c3 c2 cl cO )

The second word of each key event contains a key-down

velocity and a note duration. The note duration is stored in the

lower 10 bits (n9...n0) and can range from 0 to 1023 clock

ticks. If the duration of the note is longer than 1023 clock ticks,

the 10 bits are set to zero and another word is added to the

event. The third word ( cE...cO) can contain note durations up

to 32767 clock ticks (remember the MSB is cleared and can't

be used). The velocity is stored in the 5 remaining bits of the

second word. This brings up another limitation of the VFX-SD

and SD-1 sequencer formats. MIDI note velocities can range

from 0 to 127 giving 128 possible velocities. The VFX-SD and

SD-1 sequencers can only store 32 different velocities. To

allow for the full MIDI range, Ensoniq converts the 32 values

into every fourth MIDI value (0,4,8,12...). If you edit the

velocity of a note in a sequence, it will be changed to the

nearest value allowed.

Poly Key Pressure Events 88 -175 (58 - AF hex)

The next 88 event types (88 - 175) (58h - AFh) refer to the

poly key pressure (aftertouch) for the same 88 keys (AO - C8)

on a piano. To obtain the key number, subtract 88 from the

event type. This event type stores the entire midi pressure range

in the lower 7 bits (p6...p0) of the second word. The remainder

of the second word is not used and is set to zeros.

MSB

Word 1: 1 d6 d5 d4 d3 d2 dl dO

W o r d 2 : 0 x x x x x x x x x x x x x x

LSB

t7 t6 t5 t4 t3 t2 tl to

X X p 6 p 5 p 4 p 3 p 2 p i p O

Controller Events 176 - 199 (BO - C7 hex)

The next event types (176 - 199) (BOh - C7h) refer to the con

troller events for midi controllers. Not all of the controller

event types are deﬁned at this time. The controller events store

the MIDI controller value in the lower 7 bits (v6...v0) of the

second word. The remainder of the second word is not used and

is set to zeros.

MSB

Word 1: 1 d6 d5 d4 d3 d2 dl dO

W o r d 2 : 0 x x x x x x x x x x x x x x

LSB

t7 t6 t5 t4 t3 t2 tl to

X X v 6 v 5 v 4 v 3 v 2 v l v O

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 31 32

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Radio Shack FX2 User Manual Page 18

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