Owner`s manual

This chapter is about the facts – physical, mathematical, and auditory – that make the TimewARP

2600, and the hardware that it emulates, possible. We have to spend a few minutes here distinguishing

between physical signals, and the sounds that people hear in the presence of certain kinds of

signals.

This is important because synthesizer equipment can only deal with signals – physical commotion

of one sort and another. When you are  ddling with synthesizer equipment, you are generating and

modifying signals for the sake of the interesting (we hope) sounds you hear when those signals reach

your eardrums.

3.1

Signals and Sounds

A signal is something happening: a waving  ashlight, ambulance siren, referee  ag

dropping, winking at a friend. Tiny disturbances of the air around us are signals for our

ears; we hear them as noise, or singing, or sirens, shrieks, growls, whatever.

The

signal

is the physical disturbance in the air, the movement of the eardrum. The

sound

is your perception of the signal: “Hello!”

3.1.1

Analog and Digital Representations of Signals

The signals we are concerned with in sound synthesis are

audio

signals: more or less

regular variations in air pressure, at our eardrums, repeating at rates of between 20 and

20,000 times in one second.

Such signals are straightforward physical processes which can be recorded and

reproduced. One way to do that is to look at the pattern of air-pressure variation, and

model it in some other medium. During the past century this has been done with grooves

in a phonograph record, magnetic  elds along a length of tape or wire, and other media.

The usual scenario is: with one or more microphones, generate an electronic model

of the vibrating air, then use the electronic signal to drive a magnetic recording head,

or ampli er, or LP recording lathe. Throughout such processing, the signals we deal

with are directly analogous to each other; except for the change in medium from air to

voltage to magnetic  eld strength or stylus position, the signals are identical. Graphed

or charted, they even

look

the same. This is

analog

recording.

analog recording.analog

The Craft of Audio Synthesis