A quick example of this (on a commonly used program):
1. Using WinISD Pro; go to the Transfer Function Magnitude (EQ Filter) menu (after loading a speaker file)
2. Using REW; load look at the Modal EQ with a measurement loaded, check so you can see just the filter response
3. In both programs, load a parametric EQ, with a Frequency: 1000 hz, 24 db gain, and a Q of 1.
4.Pick a frequency (I will use 2000 hz) and note the gain in each program, I get:
WinISD Pro: +18.92 db @2khz
REW: +8.9 db @ 2khz
So clearly both programs are using different methods of calculating the shape of the filter even though they both are using "Frequency" "Gain" and "Q".
EDIT: I realize that this is all in 'software' however depending on the calculation method of the device you are programing you could have a large difference between what you 'should be getting' (according to REW) and what you are actually getting; at least at frequencies other than the center frequency
EDIT/addition 2: I have noticed also that as the frequency is increased on the filter and approaches the Nyquist limit (the maximum frequency representable by the sampling rate) the symmetry is not maintained by the filter (make a filter at 10khz and notice how the half on the 20khz side is 'steeper' than the 5khz side; this is a simulation of how most digital filters work however some manufacturers/products do correct for this (the Crown USM-810 I use being one of them... I called and asked
) so that is just another thing to be aware of when designing filters.
1. Using WinISD Pro; go to the Transfer Function Magnitude (EQ Filter) menu (after loading a speaker file)
2. Using REW; load look at the Modal EQ with a measurement loaded, check so you can see just the filter response
3. In both programs, load a parametric EQ, with a Frequency: 1000 hz, 24 db gain, and a Q of 1.
4.Pick a frequency (I will use 2000 hz) and note the gain in each program, I get:
WinISD Pro: +18.92 db @2khz
REW: +8.9 db @ 2khz
So clearly both programs are using different methods of calculating the shape of the filter even though they both are using "Frequency" "Gain" and "Q".
EDIT: I realize that this is all in 'software' however depending on the calculation method of the device you are programing you could have a large difference between what you 'should be getting' (according to REW) and what you are actually getting; at least at frequencies other than the center frequency
EDIT/addition 2: I have noticed also that as the frequency is increased on the filter and approaches the Nyquist limit (the maximum frequency representable by the sampling rate) the symmetry is not maintained by the filter (make a filter at 10khz and notice how the half on the 20khz side is 'steeper' than the 5khz side; this is a simulation of how most digital filters work however some manufacturers/products do correct for this (the Crown USM-810 I use being one of them... I called and asked
) so that is just another thing to be aware of when designing filters.
