Digital audio formats Flashcards
What is audio data commonly stored as?
A sequence of integers to represent the waveform.
What is bit depth?
(or bit resolution) governs the amount of storage required for each sample.
What is PCM?
Pulse Code Modulation
The “standard”, raw, uncompressed audio data transmission and storage format
What is the ‘pulse’ in PCM?
“Pulse”, because amplitudes are sampled/played back at regular intervals.
What is ‘code’ in PCM?
“Code”, because the amplitude is stored as a number.
What is ‘modulation’ in PCM?
“Modulation”, because the numbers represent changes (in amplitude) over time.
What is PCM the default format of?
WAV and AIFF audio files.
How do you convert bits per sample to bytes per sample?
Divide by 8 (needed when calculating file size)
How do you calculate 1 minute of CD audio in MB?
44100 x 16(divided by 8) x 2 x 60 then divide the answer by 1024 squared.
How do you work out the bitrate/bandwidth required for PCM audio?
sample rate(44100) x number of bits per sample(16) x number of channels(2)
How are multiple channel files usually stored?
By interleaving samples from each channel
- (A stereo-interleaved file is stored:
LRLRLRLRLRLRLRLRLRLRLRLRLR)
What is a frame?
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]
How is data usually structured?
In a container format, that includes identifiers and meta-data (includes a header, with information about the data)
When was IFF developed?
The Interchange File Format was developed by Electronic Arts (and Commodore) in 1985.
What is IFF?
A generic container format where different types of information are divided into different areas of the file known as chunks (headers + binary data)
What does IFF form the basis for?
Forms basis of both AIFF and WAV:
In audio files, what are there chunks for?
- 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.).
What does every chunk start with?
Chunk ID stored in four human readable character bytes e.g., ‘data’, ‘fmt’ or ‘cue’
What is the chunk ID followed by?
A 32-bit (4-byte) unsigned integer stating how many bytes are to follow.
What do applications use chunk ID and size for?
To skip data they do not need or can’t support.
Which endian do most modern computers use?
Little Endian - Each byte of a ‘word’ is stored LSB first and MSB last
i.e. the “Little End” is first
How many minutes can you fit on a CD compared to vinyl
CD = 74 mins Vinyl = 64 mins
