Question

The process of converting analog signal to digital signal is called

Answer 1

It is called Analog to Digital conversion. It happens as follows.

Pre-amplification - increase the signal strength to a sufficient level. Eg. Audio from a microphone in few milli volts is preamplified to few volts.Filtering - Remove the unwanted frequencies from the signal to save bandwidth. Eg. Audio signal is filtered with a low pass filter that pass only less than 20kHz (Human audible bandwidth).Sampling - converting a continuous wave of analog signal to discrete pieces or samples for recording digitally. The number of samples recorded per second is called sampling rate. Usually denoted in Hz or for audio, in kHz. Eg (144kHz). A common rule of thumb is to keep the number of samples at a minimum of twice the highest frequency of the signal. So for Audio, the minimum sampling rate must be 2x20=40kHz or more commonly, 44kHz.Quantization - Converting the captured sample values from possibly infinite number of levels to their closest defined levels. Say, the audio signal from filter has a peak to peak value of 2V. So any random sample from that signal can have the value of -1V or +1V, or any of the infinite possible values that lies in between. To record and reproduce all those possible values, we need to record them using infinite number of bits - for each sample. Clearly, such a effort is impossible and unnecessary. So, we decide to record a certain number of possible values each sample can have. This is usually limited by the number of bits used per sample to record its value. For Eg: if each sample is recorded with 4 bits, a sample can have a value among 2^4=16 possible values, between the lowest and highest value. This, along with sample rate defines the quality of captured digtal signal. That is, if we convert the digital signal back to analog, how close will the reconstructed analog signal be to the original.Digitization - The quantized samples are fed to the input of an A-D converter. The circuit produces digital output based on the value of input sample which is then recorded for processing by a computer.