The goal of digital audio processing is to convert an analog signal into a sequence of numbers which can be stored and played back for reproduction.
The analog to digital process starts with an analog signal, usually a microphone preamp. The analog signal is run through an analog-to-digital converter, ADC, which takes measurements of the instantaneous voltage from the analog signal, or amplitude, at regular intervals, known as sampling.
At each sampling point, the signal is assigned a sequence of binary numbers, which is called the quantization value. Through a process called channel coding, the signal is then further encoded to eliminate any errors that might have occurred in the storage or transmission of the signal.
If the analog signal was not already band limited, an anti-aliasing filter is applied before conversion. Aliasing occurs when digitalizing a signal whose frequency is greater than the Nyquist frequency.
Once the signal has been sampled in the ADC, the digital signal may be altered in a process called digital signal processing. This is where the signal may be filtered or have special effects applied, such as; reverb, delay, chorusing and flanging.
The digital audio signal may then be stored or transmitted. Storage for digital audio comes in several forms:
- A hard drive
- USB flash drive
- Compact Flash
- Compact Disk, or CD
- MP3 player
- Or, any other data storage device
Digital audio can also be streamed to other devices.
An overview of the digital to analogue conversion process
Since the goal of digital audio processing is to recreate sound, the digital signal has to be converted back to an analog signal by means of a digital-to-analog converter, DAC. The new analog signal is then amplified and converted into a sound wave by a loud speaker.
NOTE: Sometimes, the audio signals originate in the digital domain like those created by digital synthesis. In that case, the analog to digital conversion does not take place.