These notes on Music Technology were originally written as handouts for students on examination courses at a further education college in England.
Music technology might be defined as any form of technology which helps a musician to make music.
Technology is the application of science (ie.applied mechanics, applied electricity, applied magnetism and applied acoustics).
A simple definition of music is "a pleasing combination of sounds." Music could also be defined as the art of expressing emotions in sound. Western European music consists of 5 elements (pitch, rhythm, dynamics, melody and harmony). Not all of these need be present at the same time but often are.
Music technology predates the electric era but this course is limited to creating and reproducing music with the aid of electronic instruments such as synthesizers, sequencers and samplers.
FM synthesis
When you have completed this section you should have a basic understanding of FM synthesis and know something about..
Synthesis = building up; putting together; making a whole out of
several parts.
Modulate = to vary some character of a wave form
eg.to vary its amplitude or frequency.
Frequency Modulation = changing the frequency of a wave by applying
a varying signal (usually a varying voltage)
to the oscillator producing the wave.
LFO = a Low Frequency Oscillator which operates at sub-audio freqs.
Oscillator = apparatus (eg. an electronic circuit) which produces a
constantly repeating ("periodic") wave form.
A musical sound (or "voice") can be created by combining the outputs of two sine wave oscillators. The two simple sine waves combine to give a more complex wave ie. a wave with a fuller harmonic structure.
When you play a note on an acoustic musical instrument the level of the sound rises to some value, then eventually dies away. The sound level thus changes over a period of time and the way the level changes is characteristic of the particular instrument being played. This characteristic loudness profile is called a " volume envelope" .
The quality of a note also changes as the sound decays. The harmonics
which give the note its characteristic quality or "timbre" die away at
different rates. This change in the sound quality as the note ages is
called the " timbre envelope ".
So each voice has a volume envelope and a timbre envelope. The shape of
a piano's envelopes is different from those of say an organ or trumpet.
Therefore to create realistic musical sounds or "voices" two sorts of
"generators" are needed....
In the FM synthesis system developed by Yamaha each digital sine wave oscillator is combined with its own envelope generator to form an operator . The output of one operator can be fed to the input of a second operator. From two such operators a diverse range of complex wave forms can be obtained.
With four operators there are 8 different configurations of operator relationships:
Each configuration of operators is called an algorithm . The next time you look at a synthesizer, see if the algorithms are printed somewhere on the instrument. The Yamaha DX7, for example, has 6 operators giving 32 possible algorithms.
As you can see, operators can be connected vertically, horizontally or in
configurations of both. When two operators are connected horizontally their
outputs simply add together. When they are configured vertically ("stacked")
the output of one operator modulates the input of the other.
The operator at the bottom of a stack is called the carrier. It carries the signal.
All the operators in the same stack above the carrier are called modulators.
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Sampling
When you have completed this section you should know some of the ways samplers can be used and know something about..
Program Number 6 = Bank 6. Program Number 7 = Bank 7. Program Number 8 = Bank 8. etc. The sound in Bank 8 (for example) could be played when a MIDI control message for Program No.8 is sent from the controller.
Plays 1,2 +3 then repeats 2 + 3 endlessly
sampled:
plays:
When you are satisfied with your edit points the unwanted parts of the sample should be discarded to regain storage space in the memory.
A "handshake" connection is required for bulk data transfer.
Handshaking:
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Sequencing
When you have completed this section you should know something about...
The computer based sequencer is superior in the vast number of facilities it offers. Whether the average musician uses half these facilities is another story. A personal computer plus software package is cost effective since the computer can be used for other tasks. Also the the computer can be retained when the sequencer is upgraded or replaced. Neither the computer nor the sequencer can make musical sounds by themselves. Computer based systems therefore require a synthesizer which can either be placed within the computer case or external to it.
A stand-alone dedicated sequencer serves no function other than sequencing. It can be robust and portable but cannot easily be upgraded. Usually they have small LCD screens which, when programming the unit, are not as easy to read as a computer's VDU.
A synthesizer with built in sequencer usually has fewer features than a personal computer based system but , being robust and portable, is better suited to live performance.
As well as this basic recording facility, sequencers usually have many other useful features....
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The MIDI system was introduced in 1982 to...
Data is placed on the output of the sending device one bit at a time.
The receiving device collects the coded messages one bit at a time and
reassembles the the bits into complete bytes. In addition to coded
messages the sending device also sends timing signals so that the
receiving device knows which bit belongs to which byte. The timing
signals are sent on the same line as the messages.
A MIDI signal consists of a start bit (a timing signal) 8 data bits and a
stop bit (another timing signal). A single MIDI instruction might
consist of 1, 2 or 3 of these byte groups. The rate of transmission is
about 3,000 bytes per second (31.25 kilobaud).
The current in the MIDI cable wires drives an opto-isolator . The
opto-isolator consists of a light emitting diode and a photocell
contained in an opaque case. The incoming signal is transmitted by the
LED a pulses of light and converted back to a pulsating current by the
photocell.
The opto-isolator is situated at the receiving end of the
MIDI link. It enables data to be sent from one device to another
without a direct electrical connection. The isolator prevents damage
to sensitive microprocessor circuits in the event of the chassis of the
equipment being at different potentials (voltages).
The signal wires are connected in the plugs to pins 4 and 3. The cable screen is connected to pin 2 of each plug. In the equipment, pin 2 is only connected at the send socket (MIDI OUT, MIDI THRU). Pin 2 is not connected at the receiving equipment's socket (MIDI IN) .
Using this system, a number of instruments can be connected in a chain
and each will receive a full 5mA current.
When the IBM PC was introduced (1981) serial interfaces were slower
than they are today. The rate was much too slow for MIDI. Other
personal computers (PCs) such as the Apple Mac' and Commodore Amiga
came onto the market later and could handle the MIDI data rate. All they
needed was a buffer to convert RS 232 voltage levels to a 5mA current
loop signal. The Atari ST even had a converter built in.
In order to use the IBM PC (or one of its many clones) a MIDI interface card is required. This printed circuit board plugs into one of the expansion
slots within the computer. These interface cards can be made more
intelligent than the simple converters found in other computers. They
can for example take over some of the work which would otherwise have
to be carried out by the computer's main processor.
More about MIDI
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Musical Instrument Digital Interface
When you have studied this section you should know...
Introduction: the need for MIDI
MIDI is a means of communicating between two or more suitably equipped
electronic musical instruments. Before MIDI was introduced it was
possible to swop information between analog instruments. It was common
for two analog keyboards to be connected together so that both machines
could be played from one keyboard, providing a richer, enhanced sound.
The usual method of connecting two analog synths. was the GATE/CV
method. The gate signal simply turned a voltage on or off. This gate signal was obtained from switches beneath the piano-type keys. The gate voltage was normally about 0 volts, switching to about 5 volts when a key was pressed.The pitch of the note was determined by the
Control Voltage. One standard was a control voltage (C.V.) of 1 volt
per octave . If 3v produced middle C then 4v produced the C an octave
higher. This logarithmic scaling allowed a wide range of notes to be
produced without a wide voltage range being necessary.
A polyphonic synthesizer can play several notes simultaneously
eg, 16 notes. However a large number of wires are required to
interconnect two polyphonic analog synths. With 16 note polyphony, for example, 32 wires are required just to switch notes on and off!
.eliminate the mass of interconnecting wires
.allow a wide range of instruments to work together
.allow systems to be upgraded (to take advantage of new
developments without having to scrap existing equipment).
MIDI overcomes the rapid obsolescence caused by constant developments
in consumer electronics.
The MIDI signal
MIDI is a purely digital system and it does not rely on a varying voltage
to indicate the pitch of a note, or anything else. The signal carrying
the information is either at logic 0 or logic 1. One digital signal on its own simply acts as an on/off switch. Several on/off signals are
grouped together to to convey information. The individual on/off
signals (logic 0, logic 1) are called bits .
A group of 8 bits is called a byte . An 8 bit "byte" can form any
number from 0 to 255 and each number can be used as a code.
A group of bytes may be used to send a complex message.
The MIDI link
The MIDI connection is a loop, around which a pulsed current flows.
When no information is being transmitted the current is steady at about 5mA. This drops to 0mA when a start bit is transmitted and returns to 5mA when a stop bit is
sent. Each of the 8 data bits in between might be at 0mA or 5mA.
The MIDI cable
The standard MIDI connection is via a screened cable with two signal
wires and a 5 pin DIN plug at each end. The 5 pins are arranged in a 180 degree arc .
(There are 5 pin DIN plugs with other pin configurations).
MIDI THRU
The MIDI system works by switching a 5mA current on and off. If two or
more instruments were connected to the output of a single controller
(eg. a keyboard) the current would be shared between the controlled
instruments.
There might be too little current for them to operate correctly. The
MIDI THRU provides an additional output socket. This MIDI THRU socket
is supplied through a buffer amplifier with a signal from the MIDI IN
( not the MIDI OUT). The buffer amp. supplies a current of 5mA to the
MIDI THRU socket.
THRU Box
A THRU BOX provides a number of THRU sockets in one unit. It allows
MIDI instruments which do not have THRUs to be used in a
multi-instrument set-up. Instruments are connected to the THRU BOX in a
star configuration.
Expanders
These are electronic musical instruments with no means of control eg.
no keyboard. They are often rack-mounted and controlled from a remote
keyboard, wind controller, guitar controller or computer etc. MIDI interface
Serial data transmission is widely used in computing (eg. the RS 232
system). MIDI is faster than the system used for computing and differs
in another respect. The RS 232 computer system uses +12v for logic 1
and -12v for logic 0. MIDI, as we've already seen, uses a current
switched between 5mA and 0mA.
MIDI equipment cannot,therefore, be directly connected to the serial
output ("port") of a computer. An interface is required.
The interface consists of two parts; hardware and software. The hardware
("card") is the electronics required to pass information between
machines. The software encodes the data, turning complex instructions
into simple digital signals.
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[F.M.Synthesis]
[Sampling]
[Sequencing]
[MIDI]
[ MIDI Modes]
[MIDI Timecode]
