Audio Signal Processing and Coding

1.6 NOTATIONAL CONVENTIONS

Unless otherwise specified, bit rates correspond to single-channel or monaural coding throughout this text. Subjective quality measurements are specified in terms of either the five-point mean opinion score (MOS, Table 1.3) or the 41-point subjective difference grade (SDG, Chapter 12, Table 12.1). Table 1.4 lists some of the symbols and notation used in the book.

Table 1.3. Mean opinion score (MOS) scale.

MOS	Perceptual quality
1	Bad
2	Poor
3	Average
4	Good
5	Excellent

Table 1.4. Symbols and notation used in the book.

Symbol/notation	Description
t, n	Time index/sample index
ω, Ω	Frequency index (analog domain, discrete domain)
f(= ω/2π)	Frequency (Hz)
Fs, Ts	Sampling frequency, sampling period
x(t) ↔ X(ω)	Continuous-time Fourier transform (FT) pair
x(n) ↔ X(Ω)	Discrete-time Fourier transform (DTFT) pair
x(n) ↔ X(z)	z transform pair
s[.]	Indicates a particular element in a coefficient array
h(n) ↔ H(Ω)	Impulse-frequency response pair of a discrete time system
e(n)	Error/prediction residual
	Transfer function consisting of numerator-polynomial and denominator-polynomial (corresponding to b-coefficients and a-coefficients)
	Predicted signal
Quantization/approximation operator or estimated/encoded ...