BeginnerTopic 25 of 101Signals, Control & Comms
Quantisation
Rounding samples to finite levels introduces quantisation noise.
In depth
Quantisation maps continuous amplitudes to 2ᴺ discrete levels, introducing error with uniform distribution of variance Δ²/12. SQNR≈6.02N+1.76 dB for a full-scale sine. Non-uniform (μ-law, A-law) quantisers suit speech; dithering decorrelates error.
Key points
- Step size Δ=range/2ᴺ
- Clipping
- Noise shaping
Example16-bit audio has about 98 dB dynamic range.
What is Quantisation?
Rounding samples to finite levels introduces quantisation noise.
Why is it important to understand quantisation?
Quantisation adds rounding noise when continuous values are stored in finite digits, which limits the accuracy of every digital measurement.
What is quantisation noise?
The error from rounding each sample to the nearest level, which for an ideal converter has a power set by the step size.
What does each extra bit give?
About six decibels more signal-to-quantisation-noise ratio, so the resolution improves steadily with bit depth.
How is Quantisation used in practice?
Typical applications include estimating the noise floor of a 12-bit ADC in a measurement system, choosing the number of bits for an audio recording and deciding whether a sensor reading needs dithering to show small changes.
What should I learn before Quantisation?
Study "Aliasing" first (topic 24 of 101 in Signals, Control & Comms). It covers the groundwork this topic builds on.
What are the key points of Quantisation?
Step size Δ=range/2ᴺ. Clipping. Noise shaping.
Can you give an example of Quantisation?
16-bit audio has about 98 dB dynamic range.
What comes after Quantisation?
The next topic is "Discrete-time Fourier transform", which builds directly on this one.
How difficult is Quantisation?
It is classed as Beginner in Signals, Control & Comms (topic 25 of 101). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.