Sampling analogue sound
What is Sampling?
Sampling is the process of converting an analogue sound signal into digital form by taking measurements of the signal at regular intervals. Each individual measurement is called a sample. A sample captures the amplitude - the height of the wave at that precise moment in time - and records it as a binary number.
Because a computer can only store a finite sequence of values, the continuous analogue wave must be reduced to a series of discrete snapshots. The more frequently samples are taken, the more closely the digital version follows the shape of the original wave, and the more faithfully the sound can be reconstructed during playback.
The binary number stored for each sample represents the amplitude value, rounded to the nearest available digital level. A sequence of these numbers, stored one after another, forms the digital audio data. During playback, a DAC reads the sequence and reconstructs an approximation of the original wave.
How Sample Rate Affects Quality
The sample rate is the number of samples taken per second, measured in hertz (Hz) or kilohertz (kHz). A higher sample rate takes more snapshots per second, producing a more accurate digital representation of the wave shape.
Low Sample Rate
When samples are taken infrequently, large portions of the wave between samples are not recorded. The digital version can only reconstruct a rough stepped approximation. High-frequency details in the sound - rapid changes in the wave - are completely missed. This produces audio that sounds muffled, distorted, or unrecognisable compared to the original.
High Sample Rate
When samples are taken frequently, the digital version closely follows the shape of the original wave. Rapid changes are captured, fine detail is preserved, and the reconstructed audio sounds much closer to the original. The standard sample rate for CD-quality audio is 44,100 Hz (44.1 kHz) - meaning 44,100 amplitude measurements are taken every second.
Key Takeaways
- A sample is a single measurement of the amplitude of an analogue wave at one specific point in time.
- Sampling converts a continuous analogue signal into a sequence of discrete binary numbers by taking these measurements at regular intervals.
- The sample rate (measured in Hz or kHz) determines how many samples are taken per second. A higher sample rate produces a more accurate digital representation.
- A low sample rate misses rapid changes in the wave, producing a poorer quality digital recording. CD-quality audio uses 44,100 samples per second (44.1 kHz).