UNDERSTANDING: Transient considerations

PS AUDIO / Paul McGowan

There are a lot of parameters audio design engineers must consider when crafting a new amplification circuit.

Chief among them is the dynamic ability of a circuit to properly reproduce transients.

Transient response in an audio system refers to how quickly and accurately the system responds to changes in the audio signal, particularly fast, brief changes. Take for example the pluck of a string or the blat of a trumpet.

If we were to resort to a car analogy it might be described as how quickly one can go from zero to 60.

Staying with that analogy, it should be obvious that there is a finite time required to go from zero to whatever. Also, what happens when you get to 60 mph? In an audio circuit, it’s important to be able to move from a zero state to a loud state and then back again. Think of what happens when a drumstick strikes a drum head. Quick on, quick off.

As engineers, we look at some pretty well defined parameters when considering transient response. They include:

  • Rise time: This is the time it takes for an audio signal to rise from 10% to 90% of its maximum value. A faster rise time results in a more defined transient response, allowing for more accurate reproduction of fast-changing signals.
  • Slew rate: This is the rate of change of the output signal over time, and it is directly related to the ability of the system to respond to changes in the input signal. A higher slew rate means the system can respond more quickly to changes in the input signal.
  • Overshoot: This is the amount by which the output signal exceeds the final steady-state value. Too much overshoot can result in distortion, while too little can result in a lack of detail in the transient response.
  • Settling time: This is the time it takes for the output signal to reach its final steady-state value after a change in the input signal. A shorter settling time results in a more accurate transient response, while a longer settling time can result in smearing or blurring of the transient information.

Like harmonic or intermodulation distortion, any loss or modification of the signal’s transient response impacts sound quality.

For those enamored with choosing which audio gear to buy based on measurements, this is but one example of an important factor in sound quality that is almost never mentioned or quantified in published measurements.

Just sayin’.


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