The most common active electronic component used in audio engineering is an operational amplifier often referred to as an op-amp. The settling time of an amplifier is defined as the time it takes the output to respond to a step change of input.
Settling time 5µs (black), 1µs (blue)
An Audio signal requires a fast settling time due to the signal constantly changing. Errors due to settling time produce noise level, non-harmonic distortion, (not related to original signal). This noise level increases with slower settling time, this noise level is defined as a ratio between system settling time and the highest transferred frequency. The settling time of the system feedback loop must be less than 1µs (microsecond), to maintain high quality audio. If this is not maintained, the system creates and introduces noises that are not related to the original sound. This is an element of distortion added to the signal that is rarely talked about, but its effects are much more significant and dramatic in damaging the audio quality, than any losses due to harmonic distortion, a figure commonly published by most manufacturers.
The Settling time of common electronics systems used in most commercial sound systems is around 10 µs, ten times longer than it should be. The distortion, created by slow settling times is not commonly discussed by many manufacturers as they fail to understand its significance, often overlooking it in providing the technical specifications of products. Moreover the noise this distortion adds is very often mistaken for original high frequency, especially in digital technologies where it can exhibit itself as a bright, “fizzy” high end.
Settling time is less of a problem on simple signals because it occurs with addition to the higher frequency of the original signal. However, when introducing a complex signal, due to its long settling time there is now a high level of non-harmonic distortion from the many different, prolonged scrambled elements of noise, which then create a cacophony, masking the weaker original signal nuances.
That system has a low resolution.
Settling Time, Non-Harmonic Distortion
Settling time of Operational amplifiers therefore also has a large effect on a system’s ability to transfer information accurately, without non-harmonic distortion, particularly in the higher frequencies. SLA circuitry only utilizes components with settling times of 1 microsecond (1μs) or less to ensure a high definition, low distortion signal path.
Percentage of Non-harmonic distortion to various circuitry settling time
This graph shows the amount of non-harmonic distortion present in circuitry with settling time is 1μs and 10μs.
Text and photos by courtesy of KV2 Audio. All trademarks, registered trademarks and copyrights are the property of their respective owners.