Digital audio formats

Question 1

What is audio data commonly stored as?

Answer 1

A sequence of 
integers to represent the waveform.

Question 2

What is bit depth?

Answer 2

(or bit resolution) governs the amount of storage required for each sample.

Question 3

What is PCM?

Answer 3

Pulse Code Modulation

The “standard”, raw, uncompressed audio data transmission and storage format


Question 4

What is the ‘pulse’ in PCM?

Answer 4

“Pulse”, because amplitudes are sampled/played back at regular intervals.

Question 5

What is ‘code’ in PCM?

Answer 5

“Code”, because the amplitude is stored as a number.

Question 6

What is ‘modulation’ in PCM?

Answer 6

“Modulation”, because the numbers represent changes (in amplitude) over time.


Question 7

What is PCM the default format of?

Answer 7

WAV and AIFF audio files.

Question 8

How do you convert bits per sample to bytes per sample?

Answer 8

Divide by 8 (needed when calculating file size)

Question 9

How do you calculate 1 minute of CD audio in MB?

Answer 9

44100 x 16(divided by 8) x 2 x 60 then divide the answer by 1024 squared.

Question 10

How do you work out the bitrate/bandwidth required for PCM audio?

Answer 10

sample rate(44100) x number of bits per sample(16) x number of channels(2)

Question 11

How are multiple channel files usually stored?

Answer 11

By interleaving samples from each channel
- (A stereo-interleaved file is stored:
LRLRLRLRLRLRLRLRLRLRLRLRLR)

Question 12

What is a frame?

Answer 12

Each grouping that belongs to a particular moment in time is known as a frame
[LR][LR][LR][LR][LR][LR][LR][LR][LR][LR][LR][LR][LR]

Question 13

How is data usually structured?

Answer 13

In a container format, that includes identifiers and meta-data (includes a header, with information about the data)

Question 14

When was IFF developed?

Answer 14

The Interchange File Format was developed by Electronic Arts (and Commodore) in 1985.

Question 15

What is IFF?

Answer 15

A generic container format where different types
of information are divided into different areas of the file known as chunks (headers + binary data)

Question 16

What does IFF form the basis for?

Answer 16

Forms basis of both AIFF and WAV:

Question 17

In audio files, what are there chunks for?

Answer 17

• Header (sample rate, bit depth, channel, etc.)
• Audio data, Cue points (markers),
• Regions (start, end points)
• Loops (for samplers)
• Instruments (for samplers; original pitch, pitch/velocity mapping, etc.).

Question 18

What does every chunk start with?

Answer 18

Chunk ID stored in four human readable character bytes e.g., ‘data’, ‘fmt’ or ‘cue’

Question 19

What is the chunk ID followed by?

Answer 19

A 32-bit (4-byte) unsigned integer stating how many bytes are to follow.

Question 20

What do applications use chunk ID and size for?

Answer 20

To skip data they do not need or can’t support.

Question 21

Which endian do most modern computers use?

Answer 21

Little Endian - Each byte of a ‘word’ is stored LSB first and MSB last
i.e. the “Little End” is first

Question 22

How many minutes can you fit on a CD compared to vinyl

Answer 22

CD = 74 mins
Vinyl = 64 mins