[sdiy] Hardware convolution box?

[cheater00 cheater00]

Yeah, usb host mode sounds super useful unless SD will allow faster UI
interaction.

Do you know which TI chips have the most MMACS? I find the website
confusing.

On Thu, 9 Feb 2017 20:29 , <rsdio at audiobanshee.com> wrote:

> Based on your survey, I'd recommend the Analog Devices board, even though
> I usually lean towards TMS320. The TMS320 family is huge, including both
> fixed-point and floating-point, low-power and high-speed, old and new
> designs, etc. Some of the TMS320 boards you listed are really geared more
> towards motor control than audio, which is why they might be underpowered
> for long impulse response convolution. I know that the AD SHARC family is
> also large, and they're very popular, but I am less familiar with the
> options.
>
> Don't forget to look at the chip manufacturer as a direct source for these
> boards. I always buy directly from Texas Instruments because Digi-Key tends
> to have a markup. Outside the US, maybe it's a different story due to
> international availability.
>
> I'd recommend something like the 1MB 800 MMAC board and not worry about
> external RAM. 1MB seems like plenty. I'd also recommend trying to implement
> both the time domain convolution and the frequency domain version. There
> are ways to reduce the latency of the frequency domain approach, and at
> least it would allow for longer impulse responses to be supported. For IRs
> that are short enough, the time domain approach would work. I've also seen
> papers on combining the two, since LTI techniques can be run in parallel
> and summed.
>
> As for taking pairs of 16-bit samples to speed things up, be aware that
> not all instructions can work that way. I think that most DSPs can do a few
> simple operations on value pairs, but the most complex DSP instructions can
> only handle full samples. DSP architectures have internal registers that
> are much larger than the sample size, like 56-bit or higher. If you think
> about all of the potential overflow when adding thousands of samples from
> an impulse response, you can see why such large registers are needed. When
> working in that model, its not possible to handle the overflow from two
> samples that are combined in a single 32-bit input value.
>
> Finally, I think that nobody has made something like this because the user
> interface would be rather difficult. It's a bit of a power-user effect. On
> that note, some sort of SD card might be useful, so I can see why you're
> looking into that. However, perhaps just a custom USB class device would be
> enough of an interface to allow downloading impulse responses to the
> device. At a minimum, you'll need a large Flash to store the current
> impulse response, or some way to partition the program Flash to set aside
> room for the data. The AD board with USB host mode could feasibly read
> directly from a USB memory stick or Flash drive.
>
> Brian
>
>
> On Feb 6, 2017, at 9:20 PM, cheater00 cheater00 <cheater00 at gmail.com>
> wrote:
> > Brian, $50 is a steal. I've had a look at Digikey.
> >
> > This TI board is £24. It has ~150 KB on-chip RAM, but it has an
> > integrated SDRAM interface.
> >
> http://www.digikey.co.uk/product-detail/en/texas-instruments/LAUNCHXL-F28377S/296-42484-ND/5404239
> >
> >
> > This TI board is £40. It has ~384 KB on-chip RAM and an integrated
> > SRAM interface and SD card support. 200 MMACS.
> >
> http://www.digikey.co.uk/product-detail/en/texas-instruments/TMDX5505EZDSP/296-24965-ND/2127652
> >
> > This AD board is £60. It has 1MB on-chip RAM and USB host mode, no
> > idea about ram interface or SD card. 800 MMACS.
> >
> http://www.digikey.co.uk/product-detail/en/analog-devices-inc/ADZS-BF706-EZMINI/ADZS-BF706-EZMINI-ND/5408943
> >
> > This last one sports 800 MMACS. Is this enough processing power for
> > the 5-second convolution I mentioned above? It seemed to me like that
> > would need 4608 MMACs. Maybe 2304 if we take pairs of 16 bit samples
> > and treat them as 32 bit values. Are my numbers correct? Are there
> > optimizations that can be done to lower this number, while still
> > having zero latency? I understand FFT domain convolution introduces
> > latency, which is not wanted in hardware. "Naive" MAC based
> > convolution doesn't seem too far out of reach.
> >
> > This TI board is £156. It has 256 KB on-chip RAM and support for DDR2
> > SDRAM. No mention of MMACs but they say 3648 MIPS and I assume a
> > pipelined MAC costs one instruction, would that be correct?
> >
> http://www.digikey.co.uk/product-detail/en/texas-instruments/TMDSLCDK6748/TMDSLCDK6748-ND/5213032
> >
> >
> > The more expensive boards don't seem to have more powerful DSP chips.
> > And those chips don't really get much more powerful either. However,
> > convolution is easily parallelised. So, worst case scenario, if you
> > wanted really long impulse responses you'd have to use a few chips.
> > However, even the really good 800 MMACS Blackfin ones are £15 unit
> > price, so that's not so bad...
> >
> > So, tell me, why hasn't anyone made this yet?
> >
>
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