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Lab Notes: Seque and Ye Shall Find

Digital Sequencing Software

Article from Polyphony, September/October 1978


Now we're going to start a long discussion of sequencers.

It's going to be long because there is no single kind of sequencer that's best in every situation. Some will do better on stage and others will be more at home in a studio setting. Polyphonic sequencers should at times be structured for storing and reproducing chord sequences while at other times each channel should be treated as a separate voice. The only really workable solution is to come up with an entire "family" of sequencers.

The common limitation of all programming devices currently available is that none of them can offer this kind of versatility. But, this is an area where the system that we've developed, with its ability to accept a wide variety of personality endowing programs, will really come into its own. If we need a studio sequencer (with click track synchronization and full score editing features, etc.) we can load that program; when a chord sequencer is required, that software can be loaded.

These programs will all be "complete" in that once they are running, the system loses any "computer personality" that it may have had. All of the features that the program offers will be available with one or two touches of the "command" (computer) keyboard. Whereas the composer program that we did last time could only be changed by resetting the computer, using the Monitor to deposit data into memory, and running the program again (very arcane stuff, I sympathize), these programs accept all recognized commands and data "on the fly". You can forget that the computer's there because its control keys are dedicated exclusively to functions assigned them by the program. "This key makes it play — this key makes it play faster." Easy.

To illustrate these points, we'll begin with a program called SEQUE 1.0, a monotonic sequencer written to run on a PAIA P-4700/0 or its equivalent. It can also be easily patched to run on a P-4700/1 as outlined in the box.

SEQUE 1.0 is an acceptable "general purpose" sequencer (acceptable from the standpoint of our new perspective — in terms of the alternatives that are available it is the most sophisticated sequencer ever produced). It has some features tailored for live performance and others that are primarily for studio use. Altogether, it's a larger program than we can fully examine in a single story, so we'll look at the live features this time and studio features next issue. The program listing and some additional notes appear on page 18.

COMMAND KEYS



Figure 1

When SEQUE 1.0 is running, the command keys should be thought of as being labeled like this:

Keys that are not labeled are being-held in reserve for the studio operating modes. The old Monitor-assigned meanings of the keys (as shown in light type) should be ignored. To help you ignore them, a self-adhesive overlay is available.

Undoubtedly, some of the designations on the keys still seem a little on the cryptic side. Let's look at function and begin by pointing out some of the ways that SEQUE 1.0 is different from what you're accustomed to.

PROGRAMMING A SEQUENCE



The first way that it's different is that you don't program it with knobs, you simply enter the note sequence from the AGO keyboard. More specifically, the operating mode that we're looking at now is a completely "real time" performance mode. You simply touch the "PROGRAM SCORE" key and start playing. Except for the fact that we will be able to do much magic, the result is the same as if there were a tape recorder somewhere recording what you're playing. Whatever tempo you play in, including subtle timing nuances, are faithfully captured by SEQUE 1.0 and stored in the computer memory. When you reach the point at which you want the sequence to repeat, touch REPEAT PLAY and it all comes back.

PLAYING THE SEQUENCE



Since this is a real time mode, the timing of punching up REPEAT PLAY is important. If you were storing a repeating bass line, for example, you would play the single figure that characterizes the bass line and then, at the exact point (and on the beat) where the first note of the figure was to be repeated, touch REPEAT. Perhaps this is difficult to visualize (perhaps not, I've been living with it for so long that I can't tell anymore) but the first time you ever use it, you'll see how simple and convenient it is.

There are other sequencers beginning to appear that operate this way, and if real music was played with droning bass lines that repeat unchanged, endlessly, they would all be perfectly adequate. And the music would be perfectly boring.

Not that real music doesn't frequently have the characteristic of a repeating bass figure, it does, but it's also made to sound different by transposing the figure into different keys to follow key changes in the composition. While this fact seems to have been largely ignored by sequencer manufacturers, we don't have to settle for that.

TRANSPOSING



SEQUE 1.0 has a variety of provisions for transposing the programmed sequence. The simplest of these is that while in a playback mode it can accept information on key changes directly from the AGO keyboard. A little explanation.

Since we will obviously want to be able to transpose both up and down in pitch, we need to decide that some arbitrary key represents no transposition (play the sequence as programmed). SEQUE 1.0 assumes that the 2nd C on the keyboard is the "0 transpose" key. Keys up-scale and down-scale from this one, then, represent transpositions up and down scale respectively. Press the C# above the 2nd C, and the entire sequence plays with each note a semitone higher than was originally programmed. Press the F below the 2nd C and then each note plays a fifth lower.

As an example of this, suppose that we were going to want to play a walking bass line as shown in figure 2.

Figure 2
Figure 4


Figure 3

Because of the things we've talked about already, it should be relatively obvious that we only need to really "play" this much of the entire bass line:

(NOTE: Do not hit this note! Hit repeat at exactly the time you would have played it.)

...because from then on it simply repeats, transposed into different keys. As the riff from figure 3 plays, we can extend it out to the entire bass line simply by pressing keys on the AGO keyboard to perform the appropriate transpositions at the proper time. Like that shown in figure 4. Pretty exciting. And we really haven't even started yet.

THE TRANSPOSE SEQUENCE



While being able to transpose the programmed sequence with real time keyboard entries will be plenty useful again and again, there are also going to be times when it will be at best a pain in the neck. You'll be busy doing other things. For these times, SEQUE 1.0 offers another feature, the ability to save a programmed sequence of transpositions.

Programming the T-sequence (as we'll call it) is just as simple as programming the melody sequence (M-sequence), you simply touch the PROGRAM TRANS pad and enter the sequence from the AGO keyboard. The major difference from a programming standpoint is that the T-sequence is a sequence of events, which is to say that it is not sensitive to the tempo in which you enter the information. We'll talk more about EVENT sequences next time.

When the PROGRAM TRANS pad is first touched, it wipes out any previously programmed T-sequence and starts a new one. Each subsequent AGO keyboard entry then represents a key change that the M-sequence will go through at the point at which it repeats.

During the programming of a T-sequence, the displays count to show where we are in the sequence, and the note corresponding to the transposition will play while the key is held down. When the key is released, the note stops completely, so that there is no possibility of confusing this programming mode with others.

On playback, the M-sequence will be played completely through, transposed to the key signature corresponding to the first T-sequence entry; then completely through transposed by the second T-sequence entry, then the third, etc. When the end of the T-sequence is reached, the whole thing starts over again with the first note and the first T-sequence entry. To go back to our walking bass line for a moment, the T-sequence would program like this:

Figure 5


In the terms which we will find most useful, enabling the automatic transpose is an OPTION which may be selected along with one or more of the major operating MODES. If we want to assert the T-sequence option during playback, we do so by touching the T-Seq. OPTION key. To stop the T-sequence and revert to the manual entry of transpositions, simply touch the OPTION CANCEL pad.

It is important to note that canceling the T-Seq. option simply keeps the system from invoking the T-sequence, and does not in any way alter the sequence as stored. You can turn the option on and off as many times during a set as desired.

And still there's more.

SINGLE PLAY



There will be times when we don't want the sequence to repeat endlessly, but simply to play one time through and stop. A SINGLE PLAY mode.

An important difference between the two modes is that whereas REPEAT begins playing the sequence as soon as it is touched, SINGLE PLAY waits for an AGO key to be pressed and then plays.

The T-sequence option may also be asserted in the SINGLE PLAY mode, but it has been my experience that it's not tremendously useful. Much more useful is to have the T-Seq option cancelled (which selects the AGO keyboard as the transposition source), so that pressing an AGO key not only starts the sequence playing, but causes it to play in the key selected.

Releasing the key which initiated the sequence will not cause it to stop (once started it always plays to the end), but pressing a different key in the middle of the sequence will immediately transpose it to the new key signature.

TEMPO KEYS



The function of the TEMPO UP and TEMPO DOWN keys is just what you would expect. Touch TEMPO UP and the tempo of the sequence being played doubles. Touch it again and the tempo doubles again. Touch TEMPO DOWN and the tempo rate is divided in half.

If not over-used, these two keys will increase and decrease tempo while still keeping relative timing of notes unchanged; however, raising the tempo too high will cause some timing information to be lost and will cause the notes to be "jammed" together so that syncopation will change. Beware and be aware that this fact has special effects implications — there may be times when you want to do just this.

TAPE SAVES AND LOADS



The TAPE pads control a couple of operating modes which should also be useful. TAPE SAVE causes the M-sequence and T-sequence information currently in the computer's memory to be dumped to magnetic tape. When you come up with a "keeper", start your recorder going (recording) and touch TAPE SAVE. After a short leader and synchronizing tone is generated, the displays will start to count and within a few seconds your complete composition will be stored as data on the tape (a hint — always save things twice).

Loading a composition that was previously saved on tape consists of playing the tape and touching the TAPE LOAD command pad. As with the saving operation, the displays count as the data transfers from tape to memory. If, after loading a tape, you punch up a PLAY mode and nothing happens, it means that the load was unsuccessful. Try again with the second copy (and review the "tape selection" section of PAIA's 08-87 POT-SHOT manual).

NORMAL MODE



Of the MODE commands up for discussion this month, only NORMAL is left, and this is simultaneously the most straight-forward, and ubiquitous of all. NORMAL is nothing more than a normal monotonic synthesizer function, the important point is that asserting this mode of operation does not alter previously programmed M or T sequences. It simply ignores them as long as this mode is selected. At any time you can punch-up SINGLE or REPEAT PLAY and do that magic and with a touch of the NORMAL pad be back to plain synthesizer.

SUBTLETIES AND TRICKS



It seems to me that a sequencer for use on stage should have two major design goals: it should be easy to program and operate (which SEQUE 1.0 certainly is) and it should enable the user to do a better job of the thing he's there to do — put on a show. As theatrical a show as possible. SEQUE 1.0 has several of these "show" features.

The ability to shift back and forth between the various modes of operation (and specifically the availability of the NORMAL mode which doesn't mess up programmed sequences) is definitely one of these.

Others are less obvious, for example:

When you have the T-sequence option selected (so that transpositions come from their programmed sequence) and you go directly from the PROGRAM SCORE mode to REPEAT Play without first asserting another operating mode, the first entry of the T-sequence will be skipped and the melody sequence will begin playing immediately transposed by the second entry in the Transpose Sequence.

Why?

Because, when you entered the characteristic sequence it was equivalent to its being played the first time through (which would have been done using the first T-sequence entry). When you hit REPEAT PLAY and the computer takes over, it is in effect playing the sequence the second time — which should be done in the key of the second T-sequence entry.

The major application here is to allow you to enter (during set-up and tuning) a T-Sequence for the number that you're going to be doing and then enter the actual sequenced figure extemporaneously. We all know how great it is when the magic is working and everybody's really cooking. This feature allows your automation equipment to tap into that energy and the innovation that frequently results from it.

If for some reason you don't want to skip the first T-seq. entry, you simply terminate the PROGRAM SCORE mode with a command other than REPEAT PLAY (NORMAL, for instance; or SINGLE PLAY), then punch into REPEAT PLAY. Remember always, though, that the termination of PROGRAM SCORE mode must be done "in tempo" if the timing of the playback is to be correct.

Here's another special application:

In most cases, the M-sequence is reserved for the melody, but the UP TEMPO command allows you to enter some short riff (live, yet) then speed the sequence up to the point that it has the effect of being a "voice" of its own. By then punching into SINGLE PLAY mode, the sequence can then be used as you would a single note, which you "play" by transposing it. Naturally, the T-seq option should be cancelled for this.

Just one more, then the program listing.

REPEAT PLAY mode always starts the M and T sequence from the beginning, making it an easy matter to use the first: few bars of the sequence again and again, for introductions, bridges, and special effects.

Next time, we'll add studio features to this basic sequencer program and we'll probably take a look at a D/A that will allow all of our programs to be used with exponential response equipment, which should open a whole new world to owners of MOOG's, ARP's, etc.

SEQUE 1.0 COMMAND SUMMARY

PROGRAM
SCORE — Saves melody sequence in real time.
TRANSPOSE — Saves transpose sequence as events.
PLAY
REPEAT — Plays sequence from beginning, cycles until stopped.
SINGLE — Waits for key on AGO then plays sequence from the beginning. Stops at end of melody.
TAPE
SAVE — Dumps current Melody and Transpose sequences to mag. tape.
LOAD — Loads M & T sequences from tape.
OPTIONS
TABLE — Selects transpose sequence table as source of transpositions (otherwise AGO is source).
CANCEL — Turns all selected options off.
TEMPO
UP — Doubles tempo of melody sequence.
DOWN — Halves tempo of melody sequence.
MISC
NORMAL — The "normal synthesizer" mode. Does not alter stored sequences.


SEQUE 1.0

Below is a hexadecimal dump of SEQUE 1.0. Notice that the dump is divided into three sections with portions on pages 0, 1, and 2 of an 8700 memory. Before loading the program, the monitor stack pointer, User's stack pointer and status register must be pre-set as below:

0-0-E-D-Disp-F-F-Ent sets Monitor stack
0-0-F-E-Disp-F-F-Ent-0-0-Ent sets user stack and status


Setting of the stack pointer is necessary since some of the SEQUE 1.0 program is on the stack page (page 1).

With these initial parameters set, the program may be loaded as outlined in the various 8700 manuals:

0-0-0-Disp-A-9-Ent-0-0-Ent-8-5-Ent-(etc.)
for the programming on page 0,

1-0-0-Disp-8-5-Ent-1-0-Ent-8-5-Ent-(etc.)
for the programming on page 1, and

2-0-0-Disp-8-D-Ent-0-6-Ent-l-2-Ent-(etc.)
for the final block on page 2.

When the programming has been loaded and verified, it may be dumped to tape as one continuous block, if precautions are taken to once again set the stack pointers and status register as above. The tape should be dumped from $0000-$0280 as outlined in the Pot-Shot manual. These same locations should also always be pre-set when loading the tape.

Location 0 on page 0 is the starting location for the program.

%%0-0-0-0-Run

TO ALTER THE PROGRAM TO RUN ON A P-4700/J, change locations $14B & $140 as follows: 1-4-B-Disp-F-F-Ent-0-9-Ent.

A fully documented assembler listing of SEQUE 1.0 will appear in the next issue of POLYPHONY.

Note: The following is available from PAIA Electronics, Inc., (Contact Details) — complete documentation, cassette tape and plastic keyboard overlay for SEQUE 1.0 for $6.95 postpaid.


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Publisher: Polyphony - Polyphony Publishing Company

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Polyphony - Sep/Oct 1978

Donated & scanned by: Mike Gorman

Topic:

Computing

Sequencing


Gear in this article:

Sequencer > PAIA > 8700 Computer/Controller


Gear Tags:

CV/Gate Sequencer

Feature by John Simonton

Previous article in this issue:

> Electronic Music Notation

Next article in this issue:

> Polyphony Reviews


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