Yamaha PSR-S900 What is MIDI?

Using Your Instrument with

Other Devices

PSR-S900/S700 Owner’s Manual 201

What is MIDI?

Put simply, MIDI is a data transfer standard that allows

easy and comprehensive control among electronic/digi-

tal music instruments and other devices. To get a better

idea of what MIDI does, let’s ﬁrst consider acoustic

instruments, such as a grand piano and a classical gui-

tar. With the piano, you strike a key, and a hammer

inside hits some strings and plays a note. With the gui-

tar, you directly pluck a string and the note sounds.

But how does a digital instrument go about playing a

note?

As shown in the illustration above, in an electronic

instrument the sampled note (previously recorded note)

stored in the tone generator section (electronic circuit)

is played based on information received from the key-

board.

Now, let’s examine what happens when we playback a

recording. When you play back a music CD (for exam-

ple, a solo piano recording), you’re hearing the actual

sound (vibration in air) of the acoustic instrument. This

is called audio data, to distinguish it from MIDI data.

In the above example, the actual acoustic sounds of the

pianist’s performance are captured in the recording as

audio data, and this is recorded to CD. When you play

back that CD on your audio system, you can hear the

actual piano performance. The piano itself is not neces-

sary, since the recording contains the actual sounds of

the piano, and your speakers reproduce them.

In the case of digital instruments, the audio signals are sent

through output jacks (such as [AUX OUT]) on the instrument.

The “controller” and “tone generator” in the illustration

above are equivalent to the piano in our acoustic exam-

ple. Here, the player’s performance on the keyboard is

captured as MIDI song data (see illustration below). In

order to record the audio performance on an acoustic

piano, special recording equipment is needed. How-

ever, since the PSR-S900/S700 features a built-in

sequencer that lets you record performance data, this

recording equipment is unnecessary. Instead, your digi-

tal instrument allows you to both record and play back

the data.

However, we also need a sound source to produce the

audio, which eventually comes from your speakers. The

tone generator of the instrument ﬁlls this function. The

recorded performance is reproduced by the sequencer,

playing back the song data, using a tone generator

capable of accurately producing various instrument

sounds — including that of a piano. Looked at in

another way, the relation of the sequencer and the tone

generator is similar to that of the pianist and the piano

— one plays the other. Since digital instruments handle

playback data and the actual sounds independently, we

can hear our piano performance played by another

instrument, such as guitar or violin.

Even though it is a single musical instrument, the PSR-S900/S700

can be thought of as containing several electronic components: a

controller, a tone generator, and a sequencer.

Acoustic guitar note

production Digital instrument note pro-

duction

Pluck a string and the

body resonates the

sound.

Based on playing information

from the keyboard, a sampled

note stored in the tone generator

is played through the speakers.

Playing the key board

Internal amp Internal amp

Tone generator

(Electric circuit)

Recording Playback

Recording and playing back the performance of an

acoustic instrument (audio data)

Recording and play back the performance of a digital

instrument (MIDI data)

Controller (keyboard, etc.)

Recording Playback

USB storage

device

USB storage

device

Tone Generator

Sequencer

Tone generator

Sequencer

Keyboard performance (MIDI data)

What is MIDI