3rd Octave Biquad Filter Implemenation
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From: Vladimir Vassilevsky on 15 Dec 2009 11:55 Scottieb wrote: >> >>Scottieb wrote: >> >> >>>I would like to use a DSP to implement a bank of filters for a real > > time > >>>audio analyzer. The filters are 1/3rd octave spanning from 25Hz to > > 31K5Hz > >>>(32 filters). I was looking at using a C5505 to do the job, Can anyone >>>point me in the right direction to get started on implementing biquad >>>filter on this device? >> >>Start with prototyping the algorithm on PC. > > > Using Matlab or something similar? God forbid. Evaluate C or C++ code that you will later use on your target device. >>The job can be done by 8-bit micricontroller. C55xx and FPGA is >>incredible overkill; you can use *any* algorithm you like, possibly in >>the floating point. > I know you could do a low quality analyzer with an 8 bit MCU, but I would > like at least a 50Hz refresh rate on the display, so the filters need to be > giving me 1600 results ever second, not sure what that equates to in > instruction count yet, do you still think C55xx will be an overkill? For the sample rate of 96K, this could take ~tens of MIPS depending on the algorithm and the instruction set. I'd split the bands and decimate, then use Goertzel or Sin/Cos accumulation whatever is better for particular band. Anyway the load looks like too much for one 8-bitter, however it could be paralleled to more then one. Otherwise a low end DSP or bigger MCU would be adequate. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
From: Gerold Schrutz on 16 Dec 2009 04:24
"Scottieb" <scottwburr(a)gmail.com> schrieb im Newsbeitrag news:zaadnYY_WZs2H7rWnZ2dnUVZ_u2dnZ2d(a)giganews.com... > Hello All > > I would like to use a DSP to implement a bank of filters for a real time > audio analyzer. The filters are 1/3rd octave spanning from 25Hz to 31K5Hz > (32 filters). I was looking at using a C5505 to do the job, Can anyone > point me in the right direction to get started on implementing biquad > filter on this device? > > Or would I be better off using an FFT to do the job instead of biquads? > > Just a bit of background, the information with be displayed on an LED bar > graph display with 25 leds per bar for each 1/3rd octave. each led will > indicate 1 or 2dB (selectable) the display logic will be handled by an > FPGA. > > Thanks in advance for your help. > > Regards, > > Scott > > Hello Scott, A long time ago, I did such an analyser on the 56k from Freescale. It had two channels, a sample rate of 96k and update rate of 100Hz. I used a cascade structure (3x IIR's, SRC, 3x IIR's, SRC, ...) and it works quite well. So implementing a single channel analyzer on a (todays) C55xx shouldn't be a problem, but nevertheless it's not a trivial task! BR, Gerold |