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DSP Filters and slopes?
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<blockquote data-quote="Charlie Hughes" data-source="post: 27185" data-attributes="member: 474"><p>Re: DSP Filters and slopes?</p><p></p><p>What Doug is requesting is available in DSP. This type of filtering is known as FIR filtering (Finite Impulse Response). This basically (gross oversimplification follows) allows one to draw out, or otherwise specify, the shape of the filter response that is desired. The magnitude response does not have to be related to the phase response. The two can be specified separately from each other. This is different from IIR (Infinite Impulse Response) filters that are minimum phase filters. That is to say that the phase response and magnitude response are related to each other via the Hilbert transform. DSP emulation of analog LP & HP filters are IIR filters.</p><p></p><p>The price to be paid for FIR filters (there is no free lunch) is that there is increasing latency (not phase shift, but broad-band delay) through the filter as the filter frequency decreases. This is a function of the period of the filter frequency (period = 1/freq) so increasing DSP speed cannot shorten this latency.</p><p></p><p>A 1 kHz crossover frequency may not impose too much latency to be used for live sound applications. However, an 80 Hz crossover frequency may require so much latency that it is not usable for live sound. For playback applications only, this normally should not matter.</p><p></p><p>A helpful item to remember the difference between IIR & FIR LP & HP filters is as follows.</p><p>IIR filters are minimum phase, but combine to yield non-minimum phase system response (first order filters excluded).</p><p>FIR filters can be non-minimum phase, but can combine to yield minimum phase system response.</p></blockquote><p></p>
[QUOTE="Charlie Hughes, post: 27185, member: 474"] Re: DSP Filters and slopes? What Doug is requesting is available in DSP. This type of filtering is known as FIR filtering (Finite Impulse Response). This basically (gross oversimplification follows) allows one to draw out, or otherwise specify, the shape of the filter response that is desired. The magnitude response does not have to be related to the phase response. The two can be specified separately from each other. This is different from IIR (Infinite Impulse Response) filters that are minimum phase filters. That is to say that the phase response and magnitude response are related to each other via the Hilbert transform. DSP emulation of analog LP & HP filters are IIR filters. The price to be paid for FIR filters (there is no free lunch) is that there is increasing latency (not phase shift, but broad-band delay) through the filter as the filter frequency decreases. This is a function of the period of the filter frequency (period = 1/freq) so increasing DSP speed cannot shorten this latency. A 1 kHz crossover frequency may not impose too much latency to be used for live sound applications. However, an 80 Hz crossover frequency may require so much latency that it is not usable for live sound. For playback applications only, this normally should not matter. A helpful item to remember the difference between IIR & FIR LP & HP filters is as follows. IIR filters are minimum phase, but combine to yield non-minimum phase system response (first order filters excluded). FIR filters can be non-minimum phase, but can combine to yield minimum phase system response. [/QUOTE]
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