# Pulse Code Modulation PCM

Pulse code modulation is a technique, which is used to convert an analog signal into digital signal. PCM is the preferred method of within the public switched telephone network (PSTN).

It is an old but widely used concept. We need to convert our voice into digital form before transmission over long distance. Digital transmission has many advantages over analog transmission.We will discuss it after some time.

### PCM Steps

In PCM( Pulse code modulation), an analog signal is sampled and converted to a series of binary bits.It has three basic steps.

• Sampling
• Quantization
• Encoding

### Why Digital Transmission

• Less susceptible to interference caused by noise due to a discrete level.
• Easy to detect errors due to a discrete level.
• Easy to encrypt(Higher security).
• Cheaper to implement due to advancement in digital electronics.
• It is simpler to store a digital signal.

### Sampling

The function of sampling is to sample the continuous wave signal. It measures the amplitude of an analog signal at regular interval.

### Nyquist Theorem

To reproduce an original signal, the minimum sampling rate must be twice the higher frequency component of the signal.

This suggested rate of sampling is necessary for the regeneration of the signal at receiving side.

Human frequency range = 0.3 to 3.4 KHz = 4 KHz

8000 samples per second is telephony standard

### Quantization

It is the process to convert infinite value signal into a finite level.After sampling, We get a series of signal samples of multiple amplitudes.Quantization is used to limit the amplitude of these samples.

### Quantization Levels

A/D output = n bits per sample (quantization level M=2n)

8 bits = 256 levels

16 bits = 65,536 levels

### Encoding

It is just a binary conversion for a specified voltage level.

### Human Voice

Now after reading the post and watching the video, we can calculate the bit rate for human voice conversion.

Bit rate = sampling rate x number of bits per sample = 8000 x 8 = 64,000 bps = 64 Kbps

## 5 Responses to "PCM Pulse Code Modulation"

1. Sir its good vedio for telecom student

2. Why we multiply 4000*2?
What is 2 here?
My contact no is 9899784524.

By the way was a very good video.

1. Ikram Hussain

Human voice frequency is taken as 4000 hz(4kHz). Therefore 4000 is taken…. 2 is maximum possible value of bit, i.e it can be either 0 or 1. So maximum 2 is multiplied with 4000.
Hope u understand.

3. Abdul azeez

Good video by Salman Ahmad Khan saheb

1. Very good sirm