It took me a while to get my head around digital filter design algorithms. You'll need to do the following steps, which I recommend you research individually:
1. Design prototype filters, EG. "8-pole butterworth", made of poles and zeroes. 2. Transform the filters to the appropriate bandform, EG. high-pass. 3. Use a bilinear transform to move these filters to the digital domain, still poles and zeroes. 4. Compute the coefficients of the filter from the poles and zeroes. I recommend using biquad filters, each of which uses two poles and two zeroes. Step 2 or step 3 will need to involve some kind of "prewarping" to get the filter cutoff in the right location. If you don't prewarp, the filter's cutoff won't end up where you expect it to. Alternatively, here's a C++ library that does all of this, if it suits your needs: https://github.com/vinniefalco/DSPFilters – Evan Balster creator of imitone <http://imitone.com> On Fri, Dec 23, 2016 at 8:32 AM, Nigel Redmon <[email protected]> wrote: > Maybe this will help? Use four biquads, each set to the same frequency, > but with Q set as indicated by the calculator: > > http://www.earlevel.com/main/2016/09/29/cascading-filters/ > > Nigel > > On Dec 23, 2016, at 8:59 PM, Waverly Edwards <[email protected]> wrote: > > I need to apply an eight-pole Butterworth low-pass and later a high-pass > filter. Are there any built-in mechanisms for this? > > If there are not, would someone mind providing some algorithmic guidance > as to how this could accomplished? Why? I am attempting to reproduce an > experiment in which an eight-pole Butterworth filter was used -- a > high-pass at 300Hz and a low-pass at 3000Hz. If it matters, this is *not* > for iOS. > > > > Thank you kindly, > > > > > > W. > > _______________________________________________ > Do not post admin requests to the list. They will be ignored. > Coreaudio-api mailing list ([email protected]) > Help/Unsubscribe/Update your Subscription: > https://lists.apple.com/mailman/options/coreaudio-api/ > earlevel%40earlevel.com > > This email sent to [email protected] > > > _______________________________________________ > Do not post admin requests to the list. They will be ignored. > Coreaudio-api mailing list ([email protected]) > Help/Unsubscribe/Update your Subscription: > https://lists.apple.com/mailman/options/coreaudio-api/evan%40imitone.com > > This email sent to [email protected] > >
_______________________________________________ Do not post admin requests to the list. They will be ignored. Coreaudio-api mailing list ([email protected]) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/coreaudio-api/archive%40mail-archive.com This email sent to [email protected]
