Rational Acoustics



jwyatt805
April 17th, 2018, 01:15 PM
In the impulse response portion of the SMAART training, why did the psuedo-random pink noise yield the best SNR over the swept sines? What's the theory behind it, just curious?

JW

Chris Tsanjoures
April 18th, 2018, 04:33 PM
Greetings JW -

So a few things. Pseudo Random noise does not get a better signal to noise ratio than a sine sweep. However, because Smaart uses the reverse-time integration method, it is not necessary to be more than 30 dB or so into the noise floor to get accurate results. Now for the deep dive:

A peculiarity of dual-FFT-based IR measurements made with logarithmic sweeps is that distortion products in the excitation loudspeaker/SUT are washed out of the IR and show up as “pre-arrivals”. Because the DFT is a circular function, these typically end up wrapped around past the beginning of the measurement and pile up near the end of the time record. The practical implication is that you may need to make the measurement time window a little larger than you would for a matched noise measurement, to ensure that these artifacts do not intrude on the reverberant decay slope.

As regards STI measurement, IEC 60628 states that, “When using a sine sweep technique, the distortion components that are inherent within the method shall be edited out or removed from the IR before calculation of the STI can be undertaken.” It is our opinion however, that this requirement argues for the use of period-matched noise rather than sweeps for STI measurement, since the masking effect of high levels of distortion in lower-spec announcement systems can significantly affect speech intelligibility, and properly should be included in the measurement.

Basically, if a loudspeaker has any amount of harmonic distortion, than the 'sound' of that distortion should be included in the measurement and not edited out. Period matched noise accounts for this, a sine sweep does not.

fedele
October 12th, 2018, 02:41 AM
In the impulse response portion of the SMAART training, why did the psuedo-random pink noise yield the best SNR over the swept sines? What's the theory behind it, just curious?

JW


in add to what Chris write, you can take a look at this my video

https://www.youtube.com/watch?v=Q0a36wAt9kI

fedele
October 12th, 2018, 02:50 AM
Greetings JW -
...
A peculiarity of dual-FFT-based IR measurements made with logarithmic sweeps is that distortion products in the excitation loudspeaker/SUT are washed out of the IR and show up as “pre-arrivals”. Because the DFT is a circular function, these typically end up wrapped around past the beginning of the measurement and pile up near the end of the time record. The practical implication is that you may need to make the measurement time window a little larger than you would for a matched noise measurement, to ensure that these artifacts do not intrude on the reverberant decay slope.
.

a my video related to this specific topic:

https://www.youtube.com/watch?v=HdkCzPEkdjc