[Csnd] Signal offset with filters

Date	2014-09-15 23:57
From	Brentt
Subject	[Csnd] Signal offset with filters
	Hi, I notice when I use filters like lowpass2, the signal tends to get offset very badly, how does one go about remedying this? Also if someone might care to give an explanation what is going in the filtering process that causes this or point me towards an explanation it would be greatly appreciated.

Date	2014-09-16 10:31
From	Joel Ross
Subject	Re: [Csnd] Signal offset with filters
	Brentt, Do you mean offset in time or offset in amplitude (bias)? Time offset is caused by the property of filters called group delay - as filters don't just affect the frequency response so you have to be careful particularly as the modifications get more extreme. More information here: http://en.wikipedia.org/wiki/Group_delay_and_phase_delay Your only remedy would be to use a different filter but there is no panacea, these relationships are all trade offs that are inherent in the filter design. Bias on the other hand would suggest a problem with the implementation, or else an underlying bias in the original signal. Regards, Joel On 15 September 2014 23:57, Brentt wrote: > Hi, > > I notice when I use filters like lowpass2, the signal tends to get offset > very badly, how does one go about remedying this? > > Also if someone might care to give an explanation what is going in the > filtering process that causes this or point me towards an explanation it > would be greatly appreciated. > >

Date	2014-09-17 08:31
From	Brentt
Subject	Re: [Csnd] Signal offset with filters
	Thank you for the reply, I meant bias, and you are right, my raw signal was biased to begin with. I was having the same issue the last time I tried to use a filter too, but I must have been using a biased signal then also. I learned some good stuff from your reply, thank you. On Tue, Sep 16, 2014 at 2:31 AM, Joel Ross <joel.binarybrain@gmail.com> wrote: Brentt, Do you mean offset in time or offset in amplitude (bias)? Time offset is caused by the property of filters called group delay - as filters don't just affect the frequency response so you have to be careful particularly as the modifications get more extreme. More information here: http://en.wikipedia.org/wiki/Group_delay_and_phase_delay Your only remedy would be to use a different filter but there is no panacea, these relationships are all trade offs that are inherent in the filter design. Bias on the other hand would suggest a problem with the implementation, or else an underlying bias in the original signal. Regards, Joel On 15 September 2014 23:57, Brentt <brenttnewman@gmail.com> wrote: > Hi, > > I notice when I use filters like lowpass2, the signal tends to get offset > very badly, how does one go about remedying this? > > Also if someone might care to give an explanation what is going in the > filtering process that causes this or point me towards an explanation it > would be greatly appreciated. > > Send bugs reports to https://github.com/csound/csound/issues Discussions of bugs and features can be posted here To unsubscribe, send email sympa@lists.bath.ac.uk with body "unsubscribe csound"