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Representing sound
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Sound is a smooth wave, but computers can only store numbers. Sampling turns a sound into a long list of binary numbers.
Sampling
A microphone turns sound into an analogue signal: a smooth wave.
To store it, the computer measures the height of the wave many times a second. Each measurement is a sample, stored as a binary number.
The list of samples is the digital version of the sound.
To store it, the computer measures the height of the wave many times a second. Each measurement is a sample, stored as a binary number.
The list of samples is the digital version of the sound.
Sample rate and bit depth
Sample rate: how many samples are taken each second, measured in hertz (Hz). CD audio uses 44,100 Hz.
Bit depth: how many bits store each sample. CD audio uses 16 bits.
A higher sample rate or bit depth gives a recording closer to the original sound, but a bigger file.
Bit depth: how many bits store each sample. CD audio uses 16 bits.
A higher sample rate or bit depth gives a recording closer to the original sound, but a bigger file.
File size
File size in bits = sample rate × bit depth × length in seconds
(This is for one channel, called mono.)
Example: 1,000 Hz, 8 bits, 5 seconds: 1,000 × 8 × 5 = 40,000 bits = 5,000 bytes.
(This is for one channel, called mono.)
Example: 1,000 Hz, 8 bits, 5 seconds: 1,000 × 8 × 5 = 40,000 bits = 5,000 bytes.
A 10-second mono clip is sampled at 2,000 Hz with a bit depth of 8 bits. How big is it in bytes?
- Bits = 2,000 × 8 × 10 = 160,000.
- Bytes = 160,000 ÷ 8 = 20,000.
Answer: 20,000 bytes
Sound is sampled: the sample rate is samples per second (Hz) and bit depth is bits per sample. Higher values mean better quality but bigger files. File size in bits = sample rate × bit depth × seconds.
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