Sequencer
Basics
by
Don Muro
Before
we can define the term sequencer, we must first have a
basic understanding of MIDI -- an acronym for Musical
Instrument Digital Interface. The phrase "musical instrument"
is self explanatory; "digital" pertains to numbers, and
"interface" can be defined as a connection which allows
two or more devices to communicate with each other. Therefore,
MIDI can be described as a digital communication system
which MIDI-equipped instruments and equipment use to communicate
with each other.
Every
MIDI-equipped instrument contains MIDI ports (connector
jacks) and a MIDI processor which converts musical data
into digital information, the common language for
all MIDI instruments and equipment.
See Figure 1.
Figure
1: MIDI cables are used to connect the MIDI ports on electronic
instruments and equipment to other MIDI ports on electronic
instruments and equipment. In this way, MIDI instruments
and equipment can communicate with each other.
It
is important to understand that MIDI cannot transmit sound;
audio signals do not travel through MIDI cables. MIDI
cables transmit musical performance information in a digital
format. Performance information is generated by a performer's
physical movements on a musical instrument. For example,
a performer playing an electronic keyboard physically
generates performance information that describes various
components of the sound -- pitch, tone quality, loudness,
and duration. The description of these musical components
is transmitted by physical movements, such as the speed
with which each key was struck, the length of time the
keys were held, the use of volume pedals, and the use
of sustain switches. The MIDI processor inside the keyboard
instantaneously converts these physical movements into
performance information which can be stored in memory
or sent to other MIDI-equipped instruments and devices
such as sequencers.
WHAT
CAN SEQUENCERS DO?
It
might be easier to understand how this process works if
you understand a basic difference between a tape recorder
and a sequencer. A tape recorder records only the finished
product: sound. A sequencer records everything that goes
into making the sound but not the sound itself. In other
words, the sequencer records the performance information
and then on playback "tells" a MIDI-equipped instrument
what to do to reproduce the sound.
WHAT
CAN YOU DO WITH RECORDED PERFORMANCE INFORMATION?
Sequencers
make it possible to edit any aspect of performance
information. For example, most sequencers allow us to
correct wrong notes, to increase or decrease a song's
tempo, to play a song back in a different key, and more.
A sequencer also makes it possible to save or to store
edited performance information, usually on a computer
disk. This storage capability allows us to recall the
data and play back any song at a later time without
having to re-record the music. A sequencer, therefore,
is a device that can record, edit, store, and play back
digital data which represent a musical performance. (Note:
some sequencers also have the capability of recording
acoustic sounds as well as MIDI data.)
SEQUENCERS
vs. TAPE RECORDERS
Sequencers
share a few similarities with tape recorders. Both use
controls such as PLAY, RECORD, STOP, PAUSE, REWIND and
FAST FORWARD. Both store information on media: a tape
recorder uses magnetic tape, and a sequencer uses either
computer memory or a computer disk -- usually the hard
drive in a computer. But that's just about where the similarity
ends. Sequencers have many advantages over tape recorders,
which make it possible to create and to edit music in
ways which are difficult, if not impossible, when using
tape recorders.
First,
sequencers offer independent tempo/key variables. Increasing
or decreasing the playback speed of a tape recording will
change both the pitch and the tempo. Sequencers, however,
can play back a song in any key without a change in tempo.
They can also play back a song over a wide range of tempos
without changing the key.
Second,
sequencers offer easier recording techniques. A musician
using a tape recorder is limited by his or her performance
ability. A musician using a sequencer, however, can record
a musical part at a very slow tempo, then play back the
part at a faster tempo without changing the sound's pitch
or timbre. Many sequencers allow the user to type in notes
and performance data instead of playing the parts on a
keyboard. This feature is especially useful for those
who do not have strong keyboard skills.
Finally,
sequencers have extensive editing capabilities which far
surpass anything that is possible with tape. With a sequencer
it is possible to change the pitch, starting time, duration,
volume level, or tone quality of any note.
SEQUENCER
APPLICATIONS
If
you like to perform music, you can use a sequencer
to create minus-one recordings for practice or for performance.
The sequencer enables you to play back your song in any
key and at any tempo. If you like to compose music,
you can use the sequencer to record instrumental parts
one at a time to create an electronically produced rendition
of the score. In addition, you can experiment with different
tone colors by changing the sounds used for each instrumental
part. If you like to listen to music, you can use
the sequencer like a CD player and play back pre-recorded
music which is available from music publishers as Standard
MIDI Files (SMFs). (The Standard MIDI File format
is an industry standard format for saving sequence data.)
Additional SMFs are also available from the Internet.
TYPES
OF SEQUENCERS
There
are three types of sequencers: a hardware sequencer,
a software sequencer, and an integrated sequencer.
A
hardware sequencer is a discrete component which,
in some cases, contains internal sound generating capabilities.
Hardware sequencers include features such as built-in
MIDI ports and an internal disk drive for storing data.
Software
sequencers are computer programs which enable a computer
to function as a sequencer. The term "software" can be
defined as digital data which instruct computers how to
perform a particular function. At the present time there
are dozens of software sequencer programs available for
computers. Software sequencers usually consist of at least
one disk and an owner's manual. Since most computers are
not currently manufactured with built-in MIDI ports, software
sequencers require the use of a MIDI computer interface.
An interface, you may recall, is a connecting device that
allows two or more instruments or devices to communicate
with each other. A MIDI computer interface, then, is a
device which allows synthesizers and other MIDI-equipped
instruments to communicate with a computer. A MIDI computer
interface usually is an add-on component which takes the
form of a small box. A computer is usually connected (through
an interface) to a synthesizer by two MIDI cables; one
to send information and one to receive information. A
third cable connects the MIDI interface to the computer.
In
Figure 2 we see a typical setup consisting of one MIDI
keyboard, a MIDI interface, and a computer.
Figure
2: The most common MIDI setup: a MIDI keyboard, a MIDI
interface, and a computer.
In
Figure 2, there are three cable connections on the MIDI
keyboard: MIDI IN, MIDI OUT, and audio out. Remember,
MIDI cables transmit performance information about sound,
not the sound itself. In order for you to hear the keyboard,
you must connect the keyboard's audio output to headphones
or to a speaker. (If your keyboard has stereo outputs,
use both audio outputs. The sound of any sequence can
usually be improved by creating a stereo mix.)
Note:
Figure 2 shows the most common way of connecting a MIDI
keyboard to a computer. There are two other ways to do
this: a direct keyboard/computer connection, and
sound card connection. A few electronic instruments
have a built-in direct keyboard/computer connection (sometimes
called a personal computer interface). This connection
is identical to a standard MIDI IN/OUT connection; however,
it allows you to bypass an external MIDI computer interface
and to connect the keyboard directly into the computer.
The connection to a Macintosh is through either the modem
or printer port. The connection to an IBM compatible is
through a serial port.
If
you own an IBM compatible computer, you can sometimes
use the computer's internal sound card as a MIDI interface.
Many sound cards can send and receive MIDI data through
the card's joystick port. Using the soundcard as a MIDI
interface requires a special adapter cable which has a
joystick connector on one end and MIDI IN and MIDI OUT
ports on the other end.
Integrated
sequencers are sequencers which are built into electronic
musical instruments such as synthesizers, digital pianos,
and drum machines. Many of today's electronic instruments
contain powerful integrated sequencers.
WHICH
TYPE OF SEQUENCER IS BEST: HARDWARE, SOFTWARE, OR INTEGRATED?
There
is no such thing as the "best" type of sequencer. Each
of the three types has advantages and disadvantages. For
example, the advantages of the hardware sequencer
are portability and price (when compared to the price
of a computer, MIDI interface, and software). If the hardware
sequencer doesn't contain an internal sound generator,
however, you will still have to purchase and carry a MIDI
keyboard or an expander module (a synthesizer without
a keyboard). Another drawback of a hardware sequencer
is the small screen size compared to a typical computer
monitor.
The
software sequencer format is the least expensive
way to go if you already own a computer, a MIDI keyboard,
and a MIDI interface. Software sequencers range in price
from approximately US $19.00 to US $500.00. In addition,
software sequencers offer the greatest variety of features.
Some sequencer programs will print musical scores from
your recordings. Others will also allow you to record
vocals and acoustic instruments with your MIDI data. Software
sequencers take advantage of your computer monitor and
include large, graphic screen displays which use color
to help identify various recording and editing functions.
If you don't own a computer, however, you will have to
make a considerable investment to get up and running.
If portability is important, you will probably want to
invest in a laptop computer.
The
integrated sequencer's main advantage over hardware
sequencers and software sequencers is portability. Everything
you need to record, play back, and play along with your
music is in one piece. Plug in the keyboard, connect it
to speakers and you are ready to go. Like the hardware
sequencer, however, the integrated sequencer suffers from
a relatively small viewing area.
In
short, if portability is not an issue and you want to
be able to print musical scores and record acoustic sounds
with your MIDI data, the software sequencer is the way
to go. If portability is important, you can choose one
of the following options: 1) a laptop computer and a software
sequencer; 2) a keyboard with an integrated sequencer;
or 3) a hardware sequencer and a keyboard.
HOW
A SEQUENCER WORKS
Figure
3 shows how a sequencer's recording and playback functions
work. For the purpose of clarity, Figure 3 displays a
hardware sequencer with built-in MIDI ports. One MIDI
cable (the dotted line) connects the MIDI OUT port of
the synthesizer to the MIDI IN port on the sequencer.
This connection enables the sequencer to record MIDI data
generated by the synthesizer. The second MIDI cable (the
solid line) connects the MIDI OUT port of the sequencer
to the MIDI IN port on the synthesizer. This connection
enables the synthesizer to produce sound from the MIDI
data it receives from the sequencer.
Figure
3: In this diagram, the dotted line shows the flow of
MIDI data during recording. The solid line shows the MIDI
data flow during playback.
Figure
4 depicts a typical MIDI setup consisting of one MIDI
keyboard, a MIDI interface, and a computer. Let's examine
the recording and playback functions in detail.
Figure
4: A closer look at the MIDI data flow during the recording
process.
Here's
what happens in Figure 4:
Step
1 - The music performed on the keyboard is converted
to MIDI data by the MIDI processor inside the synthesizer.
In other words, the MIDI processor converts every aspect
of the performance into digital data.
Step
2 - The MIDI data from the synthesizer travel through
a MIDI cable into the MIDI computer interface.
Step
3 - The computer interface sends data into the computer
memory.
Step
4 - The data are stored permanently on a hard disk
or a floppy disk. In Figure 5, you can see how the sequencer
plays back the musical performance.
Figure
5: A closer look at the MIDI data flow during playback.
Step
1 - The data stored on a hard disk or a floppy disk
are loaded into the computer memory.
Step
2 - The computer reads the data and sends the data
out to the MIDI computer interface.
Step
3 - The data travel through the computer interface
and into the MIDI IN port of the synthesizer.
Step
4 - The MIDI processor inside the synthesizer executes
the performance information and the synthesizer reproduces
the original performance.
WHAT
TYPES OF DATA DOES A SEQUENCER RECORD AND PLAY BACK?
The
digital data traveling through MIDI cables represent messages
or commands that are expressed by a series of zeros and
ones. These zeros and ones can represent many different
types of information, depending upon the specific instruments
and devices used in a MIDI setup. We'll focus on MIDI
channel voice messages -- the type of information
most useful for sequencing. MIDI channel voice messages
can include the following information:
Note-On
- This message signals the beginning of a note. Whenever
you press a key on the keyboard, a note-on message sends
out digital information that translates into a "Start
playing NOW!" command. The note-on message also includes
information indicating how quickly a key is struck. This
information is called the velocity level, which
is often used to control the loudness and brightness of
a note.
Note-Off
- This message signals the end of a note. Whenever you
release a key on the keyboard, a note-off message sends
out a "Stop playing NOW!" command. Most sequencers display
note-off messages by listing the duration time for each
note-on message.
Program
Change - The word program is used to describe
a preset sound in an instrument's memory. A preset sound
contains specific information about pitch, loudness, tone
quality, and other properties of sound. For example, Program
1 might be a piano sound, Program 2 might be a guitar
sound, and so on. A program change message signals a program
change on your instrument. For example, when you push
a button to select Program 3 on your instrument, a program
change message sends out a "Go to Program 3 NOW!" command.
Pitch
Bend - The pitch bend change message sends information
about the pitch bend controller. Whenever you move the
pitch bender on your instrument, the pitch bend change
message sends out a stream of digital information that
represents the physical movement of the pitch bender.
Aftertouch
- Aftertouch information is generated on many electronic
keyboards by applying additional pressure to a key after
it is depressed. As the key is pressed harder and harder,
more and more information is transmitted. This information
is commonly used to increase the brightness of a sound
or to increase the amount of vibrato.
Control
Change - The control change message sends information
about a setting for a controller. Controllers include
devices such as volume pedals and sustain switches.
Note
on, note off, program change, pitch bend, aftertouch,
and control change - These are the messages used
most often with sequencers. The ways in which these messages
are generated, recorded, and edited will determine the
musicality of your sequences.
Not
all MIDI-equipped instruments can transmit or receive
all of these messages, however. For example, most MIDI-equipped
digital pianos do not use pitch bend controllers or generate
aftertouch data. The more messages that an instrument
can transmit and receive, the greater the expressive capabilities
of the instrument.
SEQUENCER
TRACKS AND MIDI CHANNELS
The
multi-track capability of sequencers makes it possible
to build multi-layered musical arrangements by recording
individual musical parts one at a time. Let's suppose
that on Track 1 of the sequencer you want to record an
electric piano part. On Track 2 you want to add a bass
part. On Track 3, you want to add a drum part. In order
to record these three parts, however, each track must
be set to a separate MIDI channel. MIDI channels
can be thought of as electronic pipelines that enable
sequencer tracks to access synthesizer sounds. MIDI data
can be transmitted and received on 16 separate channels
numbered from 1 through 16. This means that it's possible
to hear up to 16 different timbres (instrumental sounds)
using only one synthesizer. Because each track is assigned
to a separate MIDI channel, parameters such as the program
number, volume level and stereo placement can be adjusted
individually. A musical sequence which uses several different
timbres is called a multi-timbral sequence. Note:
In order for a synthesizer to play each track with a separate
instrumental sound, we need to use a multi-timbral
synthesizer. A multi-timbral synthesizer is an instrument
that can simultaneously play several programs (or sounds)
on separate MIDI channels. (Almost every electronic keyboard
available today is multi-timbral.)
Let's
review what we've just learned. MIDI messages representing
musical parts are recorded on sequencer tracks one part
at a time. Although it's possible to produce a multi-track
sequence using only one sound, we usually want musical
parts to be heard with different instrumental sounds or
timbres. To accomplish this, we must select a separate
MIDI channel and program number for each track.
DO
I NEED MORE THAN ONE SYNTHESIZER TO CREATE SEQUENCES?
The
answer to this question depends upon the music you want
to sequence. If you want to be able to hear more than
16 different timbres at once, you will need another synthesizer.
However, you may need another synthesizer even if you
don't need to hear more than 16 timbres at once. This
need is determined by the polyphony of the instrument
you are currently using. Polyphony in this context means
the number of voices (or individual pitches) that
an instrument can play at the same time. For example,
a six-string acoustic guitar is a six voice instrument;
it can play up to six pitches at once. An acoustic piano
is an eighty-eight voice instrument. The first commercial
synthesizers were one-voice (monophonic) instruments;
only one key could be played at a time on the keyboard.
As technology advanced, synthesizers with increased polyphonic
capabilities were introduced: 4 voice instruments, 8 voice,
then 16, 32 and 64 voices. Most instruments manufactured
today have at least 32 voices which means that you can
hear up to 32 different pitches at once, and that those
pitches can be assigned to as many as 16 different timbres.
This is more sonic power than many musicians will ever
need.
CONNECTING
ADDITIONAL INSTRUMENTS TO A SEQUENCER
The
two most common ways of connecting additional instruments
to a sequencer are by using the MIDI THRU port
on your primary keyboard and by using a multi-port
MIDI interface.
The
easiest way to connect another instrument to a sequencer
is to use the MIDI THRU port on your primary keyboard.
The MIDI THRU port functions as relayer. It receives a
copy of the information that is sent to the MIDI IN port,
and relays the same information to another instrument.
Figure 6 illustrates how the MIDI THRU port can be used.
Figure
6: Using multiple sound generators with a hardware or
integrated sequencer.
In
Figure 6, the MIDI data from the sequencer travels from
the MIDI OUT port through a MIDI cable into the MIDI IN
port on Synthesizer A. The MIDI cable from the MIDI THRU
port on Synthesizer A sends an exact copy of the sequencer
data to the MIDI IN port of Synthesizer B. This connection
makes it possible for the sequencer to control both synthesizers.
To complete the setup, you need to select the MIDI channels
for each synthesizer. For example, if you wanted Synthesizer
A to play on MIDI channels 1-8 and Synthesizer B to play
on MIDI channels 9-16, you need to de-activate channels
9-16 on Synthesizer A and then de-activate channels 1-8
on Synthesizer B. If you don't de-activate the channels,
you won't be able to assign instrumental sounds to specific
sequencer tracks; both synthesizers will play all of the
tracks. The most powerful way of connecting additional
synthesizers to a software sequencer is to use a multi-port
MIDI interface. Standard MIDI interfaces have one
MIDI IN port and MIDI OUT por t. Multi-port MIDI interfaces
are available with different configurations of MIDI IN
ports and MIDI OUT ports. Figure 7 shows an example of
a MIDI interface with eight separate MIDI IN and OUT ports.
This interface allows you to connect up to 8 synthesizers
to your computer. Since each synthesizer has a separate
MIDI connection, you can use any or all of the 16 channels
on each module for up to 128 MIDI channels. |
