Digital and Analogue

Analogue Vs Digital

Analogue signals are continuous, representing information through variations in amplitude, frequency or phase.
Digital signals are discrete, using numerical representations to convey information.

Analogue Signals

Analogue signals are characterised by their continuous waveform. They can have any value within a given range.
Analogue audio equipment, such as vinyl records and tape machines, capture the entirety of an audio signal, making them prized by some for their ‘warmth’ and ‘natural’ sound.
One drawback of analogue audio is that the signal can degrade over time due to physical wear and tear, and every generation of copying further degrades the signal.
Another drawback is noise. Noise can be introduced into an analogue audio signal easily, and once it’s there it’s almost impossible to remove.

Digital Signals

Digital signals use a series of binary codes (i.e., ones and zeros) to represent the analogue wave.
This data, being digital, is not subject to wear and tear and can be copied without generation loss.
Digital audio formats, such as CDs and mp3 files, are easier to store, handle, and copy than analogue formats, which has led to the widespread adoption of digital technology in music production and broadcasting.
However, in the process of digital sampling, high frequencies can be lost if a sufficient sampling rate is not used - this is known as aliasing.

Sampling and Quantisation

The conversion of analogue audio to digital audio involves two steps: sampling and quantisation.
Sampling is the process of recording the amplitude of an audio signal at regular intervals, the number of which per second is referred to as the sampling rate.
Quantisation assigns each of these sampled amplitudes to the nearest value in a set range or scale, and this scale is determined by the bit depth.

Analog-to-Digital Conversion (ADC) and Digital-to-Analog Conversion (DAC)

ADC is the process of converting an analogue sound wave into a stream of binary digits.
DAC is the reverse process, turning the digital binary back into an analogue sound wave.
ADC and DAC are essential processes within a computer’s sound card, audio interfaces, and digital audio players.

Effects of Bit Depth and Sample Rate

The bit depth refers to the accuracy of the quantisation process during ADC. Higher bit depths lead to greater dynamic range and fidelity of the recording.
The sample rate is the number of times that the audio is sampled per second. The higher the sample rate, the higher the frequency range that can be accurately captured by ADC.
It is important to select an appropriate balance for bit depth and sample rate based on the needs of the project and the limitations of the recording equipment and medium.

Understanding Nyquist’s Theorem

According to Nyquist’s Theorem, in order to completely capture all the frequency components of an audio signal during ADC, it should be sampled at least twice the highest frequency of the audio signal.
Therefore, the audio CD standard of 44.1 kHz sampling rate is based on the assumption that the highest frequency human beings can hear is around 20 kHz.

Remember that while it’s important to understand the theoretical principles of analogue and digital sound, it’s equally crucial to develop the practical skills of using both types of equipment and being able to choose the right tool for the job.