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Old 22nd December 2012, 04:21 PM   #341
pos is offline pos  Europe
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Quote:
Originally Posted by twest820 View Post
Both the TAS in the DLCP and the SigmaDSPs in miniDSPs are fixed point. (...)
Thanks a lot for that in-depth explanation!

Quote:
Originally Posted by twest820 View Post
In comparison FIR is, well, inelegant. Bruno's pointed out---and I happen agree---that if one's after good sound quality most FIR synthesis isn't really in the right direction. That'll improve over time but, at the moment, I would say the approach used on the DLCP is fairly difficult to beat and the miniSHARC isn't really competitive on quality. Price, maybe, but that hasn't been announced yet.
It depend on what kind of filtering you are doing in FIR: I think Bruno pointed out automated FIR generation (inverse response and the like) and steep slopes (with their off axis problems...).

In FIR you can actually replicate anything that can be done with IIR filters, and even keep the whole think minimal phase if you want to avoid any delay.
As you have pointed out doing filtering with only one convolution (and a direct one with the current openDRC implementation) will lead to less rounding errors than the equivalent biquad filters.

I have done a small software called rePhase that you can use to generate FIR to do all sort of filtering (linear phase Linkwitz Riley slopes of arbitrary order, among others) and manual EQ (both amplitude and phase can be EQed separately):
rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool

It is optimized to make the best use of a given number of taps, using auto centering of the impulse based on energy, and iterative optimizations to minimize deviations from target.

I which Hypex would let the user add a short FIR filter in front of the IIR filters to invert phase shifts (as per the Grimm Audio white paper, which was an inspiration for rePhase), but it looks like they decided to ditch that functionality

Last edited by pos; 22nd December 2012 at 04:25 PM.
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Old 22nd December 2012, 04:34 PM   #342
ds23man is offline ds23man  Netherlands
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BTW,

I think I am the only one to have this board and I haven't powered it up yet!


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Old 22nd December 2012, 04:37 PM   #343
Julf is offline Julf  Europe
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Originally Posted by ds23man View Post
I think I am the only one to have this board and I haven't powered it up yet!
Got mine yesterday, but been too busy to clear the lab desk....
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Old 22nd December 2012, 04:41 PM   #344
knuisje is offline knuisje  Netherlands
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Originally Posted by ds23man View Post
And you have to intergrate it on the pcb, means more space> more costs.

I think Hypex made a valid decision not to implement a state of the art USB audio streaming option. A lot of people are moaning about the price already!

BTW, with a Minidsp product you have to buy a seperate USB streaming board!

That's why it is a pity they didn't add a I2S header so you can add your own USB interface with or without I2S isolation.

Who is talking about Minidsp here? (at least Minidsp has I2S in and out headers)
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Old 22nd December 2012, 04:46 PM   #345
ds23man is offline ds23man  Netherlands
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Originally Posted by knuisje View Post
That's why it is a pity they didn't add a I2S header so you can add your own USB interface with or without I2S isolation.

Who is talking about Minidsp here? (at least Minidsp has I2S in and out headers)
But the Minidsp has a cheapo dsp chip!

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Old 22nd December 2012, 05:25 PM   #346
knuisje is offline knuisje  Netherlands
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I'm out of here. Only nonsense replies.
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Old 22nd December 2012, 09:53 PM   #347
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Originally Posted by ds23man View Post
But the Minidsp has a cheapo dsp chip!

when you say cheapo dsp chip what do you mean ?

As I see it both the AD sigma dsp and TI TAS chips compete with each other in the market place and don't win any scores when it comes to the mips department. Also the TAS part is not recommended for new designs so that doesn't say much for its popularity.
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Old 22nd December 2012, 10:35 PM   #348
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Quote:
Originally Posted by pos View Post
Thanks a lot for that in-depth explanation!


It depend on what kind of filtering you are doing in FIR: I think Bruno pointed out automated FIR generation (inverse response and the like) and steep slopes (with their off axis problems...).

In FIR you can actually replicate anything that can be done with IIR filters, and even keep the whole think minimal phase if you want to avoid any delay.
As you have pointed out doing filtering with only one convolution (and a direct one with the current openDRC implementation) will lead to less rounding errors than the equivalent biquad filters.

I have done a small software called rePhase that you can use to generate FIR to do all sort of filtering (linear phase Linkwitz Riley slopes of arbitrary order, among others) and manual EQ (both amplitude and phase can be EQed separately):
rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool

It is optimized to make the best use of a given number of taps, using auto centering of the impulse based on energy, and iterative optimizations to minimize deviations from target.

I which Hypex would let the user add a short FIR filter in front of the IIR filters to invert phase shifts (as per the Grimm Audio white paper, which was an inspiration for rePhase), but it looks like they decided to ditch that functionality
I think you'll find the TAS doesn't have any serious horsepower to implement decent size FIR filters at least not for six channels !!
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Old 23rd December 2012, 12:31 AM   #349
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Originally Posted by pos View Post
Nice! I considered writing something similar based on talking with Bruno here on DIYA about the same short FIR phase linearization mentioned in the Grimm whitepaper but was estimating a computationally prohibitive number of taps to do what I needed. So I ended up writing Cross Time DSP instead. I plugged my woofer/subwoofer channel with 7 biquads and one first order filter into rePhase and came up with 3000 to 6000 taps for redbook depending on the desired goodness of fit (maximum optimization, best of various windows). Call it 10,000 taps at the DLCP's sampling rate, stereo execution of which would maybe fit into two top end SHARCs running flat out. In comparison, the five forward time biquads I use require about 75 MACs if they're implemented with 64 bit coefficients and feedback on a 32 bit DSC like the Cortex M4. To execute that in stereo at 93.75kHz a single M4 might have to be clocked at oh, gee, perhaps 20MHz.

It's this explosion of taps at low normalized frequency that I had in mind when remarking FIR is inelegant. I quite agree the ability to run a few hundred stereo taps to phase linearize a two way XO or the mid-tweeter XO in a three or four way in forward time is useful. However, to my knowledge, it was never a goal to support such phase linearization in the DLCP.
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Old 23rd December 2012, 06:57 AM   #350
ds23man is offline ds23man  Netherlands
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Quote:
Originally Posted by Trevor White View Post
when you say cheapo dsp chip what do you mean ?

As I see it both the AD sigma dsp and TI TAS chips compete with each other in the market place and don't win any scores when it comes to the mips department. Also the TAS part is not recommended for new designs so that doesn't say much for its popularity.

Post 336 By Twest:

". Loosely speaking, the order from worst to best is SHARC floating point, SigmaDSP, SHARC fixed point, TAS3108."


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