Digital Basics

Question 1

Analog to digital converter

Answer 1

converts an analog audio signal to digital; analog signal –> anti-aliasing –> PAM (pulse amplitude modulation) –> sample and hold –> quantizing –> PCM (pulse code modulation) –> storage

Question 2

Digital to analog converter

Answer 2

converts a digital audio signal to analog; storage –> reconstruction –> resampling –> anti-imaging filter –> playback

Question 3

Codec

Answer 3

software application that encodes a digitized audio signal file into a different format, often for the purpose of reducing its size; also called compression

Question 4

PCM

Answer 4

pulse code modulation; uses a modulated pulse wave to
capture amplitude information using numerical code, which in turn represent signal amplitude
values

Question 5

DSD

Answer 5

direct stream digital; Sony’s 1 bit digital
audio coding system that uses a very high sampling frequency, used for audio representation on the Super Audio CD (SACD)

Question 6

Latency

Answer 6

delay incurred in executing audio operations between input and output of a system; low latency is best

Question 7

Redbook Audio

Answer 7

standard for CDs; max playtime is 79.8 minutes, min duration for a track is 4 seconds, max number of tracks is 99, max number of index points (subdivisions) in a track is 99 with no max time limit, International Standard Recording Code (ISRC) should be included

Question 8

Sample rate

Answer 8

number of samples per second in an audio signal

Question 9

Word length

Answer 9

size of the digital word used for the audio samples in PCM
audio (number of bits)

Question 10

Clocking

Answer 10

high-frequency signal, usually generated by a crystal-controlled oscillator, which is used as a master timer to control the events in a digital system

Question 11

Word clock

Answer 11

digital timing reference signal that is the same frequency
as the sampling rate being used

Question 12

Over

Answer 12

overloading of peaks in a digital audio signal, producing clipping of the signal and, if severe, bursts of noise

Question 13

BWF

Answer 13

digital audio file format introduced by the EBU in 1996 to facilitate professional editing and file exchange; special case of Microsoft’s wav format, but adds extra information deemed important for professional use such as titles, date, time, origination, editing data, etc.

Question 14

WAV

Answer 14

Windows file extension that indicates Microsoft’s audio file format; uncompressed

Question 15

AIFF

Answer 15

audio file format standard used for storing sound data for personal computers and other electronic audio devices; uncompressed PCM

Question 16

Lossy

Answer 16

type of audio file compression that does not recover the original signal exactly

Question 17

Lossless

Answer 17

no information is lost in the coding-decoding process

Question 18

Uncompressed

Answer 18

audio file with all the original information of the recorded source

Question 19

Headroom

Answer 19

difference in level between the highest level present in a given signal and the maximum level the device can handle without noticeable distortion

Question 20

Nyquist

Answer 20

sampling rate of two times the maximum signal frequency is just sufficient to describe that highest frequency without ambiguity; ex. sample rate of 44.1kHz for 22kHz

Question 21

Aliasing

Answer 21

if we allow frequencies higher than Nyquist frequency to enter system, violating frequencies will not be recorded, but will instead create new frequencies

Question 22

Anti-aliasing

Answer 22

low-pass filter used during the A/D process that restricts the audio bandwidth to less than half the sampling frequency

Question 23

Delta-sigma modulation

Answer 23

rather than capturing the actual momentary voltage value, each bit simply records whether the current amplitude of the moment is higher or lower than the previous one

Question 24

Dither

Answer 24

pseudorandom noise signal with a level equal to half the least significant bit added to the input audio signal during A/D conversion; ensures that if any audio signal is present at the input it will broach the necessary threshold and be rounded up and successfully encoded; also randomizes the effects of quantization at low levels

Question 25

Jitter

Answer 25

noise caused by timing inaccuracies in D/A or A/D conversion

Question 26

Superclock

Answer 26

Pro Tools uses signal at a multiple of 256 times the sampling rate for slaving devices together with low sampling jitter

Question 27

Upsampling

Answer 27

changing a session to a higher sample rate

Question 28

Downsampling

Answer 28

changing a session to a lower sample rate

Question 29

Elastic audio

Answer 29

track-based algorithm that allows you to stretch and compress audio to fit within beats and bars

Question 30

Time compression-expansion

Answer 30

Pro Tools plugin that allows the user to make audio files longer or shorter, and to shift the pitch of audio files

Question 31

Warp

Answer 31

allows creation of markers for elastic audio to stretch and compress audio

Question 32

Floating point

Answer 32

some of the bits (the mantissa) represent a whole number, while other bits (the exponent) dictate how this number is multiplied or divided; able to have a very large dynamic range this way

Question 33

Quantization error

Answer 33

difference between stairstep shape of waveform after sampling and the continuous waveform; results in wideband noise on a musical signal

Question 34

PLL

Answer 34

phase locked loop; electronic circuit consisting of a voltage-controlled oscillator and a frequency discriminator
connected in such a way that the output of the discriminator controls the oscillator; acts as a stabilizer

Question 35

PWM

Answer 35

pulse wave modulation; a method of encoding a signal
by using the length of a pulse as a measure of the height of a sample of the waveform; all analog

Question 36

SACD

Answer 36

Sony and Phillips created; uses one-bit encoding of the audio signal at a sampling rate of 64 times 44.1 kHz or 2,822,400 samples per second, eliminating the use for an anti-aliasing filter at the input and anti-imaging filter at the output; eliminates phase distortion these filters produce

Question 37

Claude Shannon

Answer 37

invented signal flow graphs

Question 38

Two’s complement

Answer 38

way to show negative binary values; use a 1 to represent a negative number on the largest number in a byte; for example, -8 is 1000 (-8+0); -4 is 1100 (-8+4)

Question 39

Flutter

Answer 39

in an analog tape recorder, if the tape speed varies above 5Hz or so

Question 40

Wow

Answer 40

in an analog tape recorder, if the tape speed varies below several hertz