filter coefficients for biquad
I’m studying the coefficients for a basic recursive LOW PASS filter (see Dodge’s book p. 210) and I’m using a0 and b1 coefficients of biquad object.
I made some experiment using an impulse as input signal, in order to verify the impulse response of the filter.
I notice in the LOW PASS filter the b1 coefficients is always a negative number, this means the first delay of the impulse should be negative (out of phase)… but the impulse response is always positive!
Does someone knows why the impulse response is always positive, although the b1 coefficient is negative?
Thanks in advance.
Internally the b coefficients are negated, so setting the value 0.99 would effectively mean -0.99. The filter formula in the help does somehow suggest it, but it is not clearly stated. You can try that out with the patch below.
----------begin_max5_patcher---------- 482.3ocyU90SCBCD.+Y3SQSedZnrAi4GDewXLEnLqBsSnnnF2mcauByMET1e hYgjV506td2uds8cWGbrrgUgQWgtA437tqiCHxHvocrCtf1jjSq.0vB1Kx3G vSrSoXMJPrBQPwcRE0EbQNSAVPZExSAE0FeAIrSyLoPInELXpqYkoTAcKuHq UctwuUpUj50ULaTi4BEdBBGSEKwna2xuU72.cHjK8ZEuhpRtmKVdWIKQYset udVDw2yzMMzzZ9GcqwhObcMMSFIadg9LKSVVrtWPDzCHB5OYCGJYyxkTHc+k ex4UP+Wznmz1O.x6nYPBaGPBiLIdqQw0YYrxMaNMMMauomHykkVWcPnZfxH6 htFoWMTvnKmlcBKm1fwCsfhLCXZaWz7iphZ.LoWMYYJfodgzzdfzz8GRjgfT Eeofle3G27IvAs4QGEbhqUJoXzUId6YRtaAvf4xhM2Yb52mSx4IOtdrYX3Yw NrkGsk+11SMVh4OUS0k+Djm46xEKPd8BoveBofyIHE4Ye7YQuTB7q95bw2eg FbnQ9tnqRVWlzEacuyh95F8TVkhKnJt9PyVJMcGktmmlxf46B+Bd5Jo9U1pe 8598JlH+QLE9+FRdiAS+uwTv42N2XJlBNhHRO3C2OE6B2cA -----------end_max5_patcher-----------
ooohhh, now I understand!!!!
Thank you very much Johan.