# Re: swept sine accuracy

```Dear James,

```
If you have noise in the system (=room) then the sweep duration primarly depends on the signal-to-noise ratio (SNR) you want to achieve. This is because usually, the maximum amplitude of the loudspeaker is limited. Further, for exponential sweeps, the SNR may depend on frequency, f.e., it's pink if noise is white.
```
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For example, we use sweeps with at least 1.5-s duration for measurements in a sound chamber (18 dB noise) to achieve an SNR of 60 dB. For such long sweeps, the frequency smearing is negligible.
```
However, I do not have a theoretical result...

br, Piotr Majdak

James W. Beauchamp wrote:
```
```Guys,

This is a not strictly an auditory question, but it could be
useful for people doing acoustic measurements. If you use a
swept sine wave to measure the frequency response of a linear
system, what is the limitation on the speed of the sweep in
terms of how accurate the result would be? I imagine it has
```
something to do with how smooth the actual frequency response is. If it has some pronounced bumps, they could be smoothed
```out if the sweep is too fast.

In practice, you could sweep at some arbitrary rate, and then
slow it by a factor of two, and if the result is the same
(within an acceptable tolerance) you could say that you've
converged on the solution.

But I'd like to have a theoretical result.

Jim Beauchamp
Univ. of Illinois at Urbana-Champaign
```