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Raspberry Pi with Piano2.1 DAC DSP and Volumio2
Raspberry Pi with Piano2.1 DAC DSP and Volumio2
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Old 9th May 2018, 11:56 PM   #61
Davey is offline Davey  United States
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Quote:
Originally Posted by mfeif View Post
Hi folks.
I'm interested in doing an active digital crossover[1] on the DSP itself, but I saw the talk about buffer length and got worried, because one thing I need to do is to delay two of the four channels by 6ms.

1: I am making some of these and would like to skip adding the stand-alone DSP unit: LXmini Challenge
Actually, you're adding 0.06mS not 6 mS. 6mS is way too much for the offset correction in the LXmini project.

Dave.
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Old 10th May 2018, 02:49 AM   #62
DonVK is online now DonVK  Canada
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Quote:
Originally Posted by mfeif View Post
I'm interested in doing an active digital crossover[1] on the DSP itself, but I saw the talk about buffer length and got worried, because one thing I need to do is to delay two of the four channels by 6ms.
I think @Davey is correct, it should be 60us, so its approx 3 samples @ 48Khz. No problem.

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Originally Posted by mfeif View Post
I'm handy with computers, but not very good with analog sound science or digital logic, so I'm having trouble decoding the TI datasheet for the relevant DAC chip on the Piano. Do those of you who have played around with PurePath and the two PCM5142's know if what I want to do is likely to work?
The DAC DSP can easily do XOs like LR4s as well as EQ. Volumio can set the DACs to "dual stereo" mode to give you 2 R and 2 L. So with the DAC DSP you can generate the R-Highpass, R-Lowpass, L-highpass, L-lowpass outputs. To load my own DSP config I just "replace" one of the existing Volumio config files.

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Originally Posted by mfeif View Post
I understand that a rpi or equivalent has plenty of horsepower to do this kind of thing in software, but I'm not sure how to get access to the BOTH dacs on the Piano that way. Perhaps someone who's got a Piano 2.1 can let me know if all 4 channels are available to ALSA?
I have not tried to get 4 independent channels via ALSA, but I have read comments indicating its not possible, they are sourced by R&L only. One idea is to keep the DAC DSP functions to the minimum, like just the XO and maybe delays. Then do the EQ for the speaker / room in the RPI. Only because the EQ probably has more iterations and may be more complex especially if you use a FIR convolution engine (mag + phase corrections).

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Originally Posted by mfeif View Post
Before I send in the money and get boards shipped from India, I was hoping to find out if what I want to do is possible; I know there's no guarantee :-)
The most difficult item to get is the PurePath GDE license from TI. If your plans hinge on this, you may want to start (and wait?) for a TI license (free) and try your ideas.
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Old 10th May 2018, 01:51 PM   #63
mfeif is offline mfeif
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This is all SUPER helpful. I feel comfortable proceeding, thanks to you both.

I've asked for a license to PurePath already, hopefully it won't take long.

@Davey, by any chance have you made LXminis with something like this (noting your familiarity with the delay magnitude).
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