Analog To Digital

Analog data is converted to digital data and then digital signal.

Digitization

Conversion of analog data into digital data.

PCM

Short for Pulse Code Modulation.

Done in 3 steps.

Sampling

Analog signal is measured at regular intervals. Must be sampled at $2f$ frequency where $f$ is the highest signal frequency, as Nyquist theorem.

Quantization

Each sample is approximated to the nearest value of the finite set of $2^n$ levels. Represented by $n$ bits. The approximation is called quantization error.

If the set of levels are placed linearly, low amplitude signals might get very low precision. To fix that:

• non-linear quantization can be used. Here, the levels are placed logarithmically. Reduces overall signal distortion.
• companding can be used. Companding means compression + expanding. Used to reduce effects of quantization noise especially in low-amplitude parts.

Encoding

Each quantized sample is converted to a binary number.

Delta Modulation

Analog input is approximated by a staircase function. The value is increased or decreased at each sample interval based on the difference between the current sample and the previous sample, which is the delta.