From: Randy Yates on 24 Jul 2010 21:19
"bharat pathak" <bharat(a)n_o_s_p_a_m.arithos.com> writes:
> what are the problems associated with FFT based filtering?
> and when should one decide to switchover from convolution
> based time domain filtering to FFT based filtering?
It depends on things like how many hardware multipliers you have
available on your target platform, but the usual rule-of-thumb is when
you get to an impulse response on the order of 100 samples or more.
Randy Yates % "And all you had to say
Digital Signal Labs % was that you were
mailto://yates(a)ieee.org % gonna stay."
http://www.digitalsignallabs.com % Getting To The Point', *Balance of Power*, ELO
From: Vladimir Vassilevsky on 24 Jul 2010 23:15
Hello Dr. Rune!
It is good to see you again. Where have you been?
From: Rune Allnor on 25 Jul 2010 04:31
On 25 Jul, 05:15, Vladimir Vassilevsky <nos...(a)nowhere.com> wrote:
> Hello Dr. Rune!
> It is good to see you again. Where have you been?
Moving house and vacation. Starting in a new job august 1st.
It will be a lot of data analysis, but not much DSP.
From: Rune Allnor on 25 Jul 2010 08:39
On 25 Jul, 03:16, Randy Yates <ya...(a)ieee.org> wrote:
> Rune Allnor <all...(a)tele.ntnu.no> writes:
> > that combine the two approaches, by doing FFT-based filtering on
> > sub-frames of a very long sequence. I suspect these methods are
> > remnants from the times when one could actually get data sets that
> > were larger than the available RAM,
> You mean like 2010? I didn't find anywhere in the OP's original query
> that limited the platform to something like a PC. And even then, as you
> yourself noted, you don't really want to do it all in one FFT.
You edited away the essential statement of mine:
> > and so needed
> > both time- and memory-efficient methods for offline processing.
I don't really see why one would want to do offline work on
embedded devices. And I can't see how overlap-add/save would
be more efficient on embedded devices, as their capacity for
efficient computations would be offset by infklexibilities /
awkwardness with respect to flexible progra control structures.
Sure, embedded devices might be able to do stuff like FFTs
very efficiently, but they would struggle with the control
loops necessary to fuse subsequent frames.
Again, the only relevance I can see for overlap-add/save these
days, is to reduce numerical noise in large *offline* work.
From: robert bristow-johnson on 25 Jul 2010 12:43
On Jul 25, 8:39 am, Rune Allnor <all...(a)tele.ntnu.no> wrote:
> Sure, embedded devices might be able to do stuff like FFTs
> very efficiently, but they would struggle with the control
> loops necessary to fuse subsequent frames.
> Again, the only relevance I can see for overlap-add/save these
> days, is to reduce numerical noise in large *offline* work.
how about a real-time convolution reverberator based on an measured
impulse response of an actual large room (like a venerated auditorium
or cathedral)? FIR with a couple hundred thousand taps?