Line Speed is simply the data rate at which serial PCM bits are clocked out of PCM encoder out to transmission line. Line Speed is dependent on sample rate and number of bits in the compressed PCM code.
Line Speed = the transmission rate in bits per second
Samples/second = Sample rate
Bits/sample=number of bits in the compressed PCM code
Eg. Determine the minimum line speed in bits/second to transmit speech signal as an 8-bit PCM.
Solution: Frequency range of speech signal is 300Hz to 3300Hz.
Therefore, highest frequency component in speech signal is 3300Hz.
Sampling rate is double the maximum frequency component of speech signal as per Nyquist Sampling theorem. So roughly assuming if highest frequency component is 4KHz, then sampling rate is 8KHz samples/sec.