EQ Biquads limitation, direct Forms and representation
Posted: Thu Nov 12, 2020 8:04 am
Hi,
Many EQ's and filters use 2p2z (two pole two zero) IIR filters, just like in Flowstone's stock modules.
With the FS implementation I do not see any limitation on the maximum/minimum values of the coefficients.
However, I know that some DSP manufacturers limit their coefficients to (example) +/- 2.0 . So a value of (-2.00001) is not possible. Claim is stability of the filter.
I wonder why is this limitation required in the DSP but not in FS. I tend to think that this limitation is required for "fixed point" presentation (say 20 or 24 bit) and not required for "very wide dynamic range" like in "32 bit floating point".
Also I know that "fixed point" representation uses "direct form 1" while "floating point" uses "direct form 2", as explained here https://www.earlevel.com/main/2003/02/28/biquads/.
But how is that related to coefficients limitation ?
Many EQ's and filters use 2p2z (two pole two zero) IIR filters, just like in Flowstone's stock modules.
With the FS implementation I do not see any limitation on the maximum/minimum values of the coefficients.
However, I know that some DSP manufacturers limit their coefficients to (example) +/- 2.0 . So a value of (-2.00001) is not possible. Claim is stability of the filter.
I wonder why is this limitation required in the DSP but not in FS. I tend to think that this limitation is required for "fixed point" presentation (say 20 or 24 bit) and not required for "very wide dynamic range" like in "32 bit floating point".
Also I know that "fixed point" representation uses "direct form 1" while "floating point" uses "direct form 2", as explained here https://www.earlevel.com/main/2003/02/28/biquads/.
But how is that related to coefficients limitation ?