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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 7th October 2017, 06:12 PM   #21
designmule is offline designmule  United States
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Quote:
Originally Posted by DonVK View Post
I spent a bit more time to actually finesse the filters this time.

The subwoofer channels (DAC#1) use a mixed RL low passed at 80Hz (BW4) and sent to both outputs. The difference this time is the use of extended precision in the coeffs. One of the problems with setting low cutoff frequencies in a digital IIR (biquad) is that the coefficients get close to unity (ie. 0.99999965) and preserving significance is a problem.

The stereo channel (DAC#0) is high passed at 80Hz (BW4) and has additional speaker EQ. The EQ curve was initially generated earlier by REW and then manually repeated here using 6 biquads. The speakers have an internal passive LR4 but the driver responses are not FR flat. This EQ curve helps that. The DSP load is at 42% utilization now.

Overall it sounds good. This means I can do active XO and speaker EQ in the DAC's DSP.
Do you mind elaborating on what you are doing with the coefficient filter? I can copy your diagram but what are you setting it to? It looks like the default is 0.0. I really don't have any idea what it does or what it should be set to. Thanks again for sharing your post with me. It's been super helpful. Matt
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Old 7th October 2017, 07:46 PM   #22
DonVK is offline DonVK  Canada
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I just wanted to connect the sub LP output to both DAC outputs. In a schematic I would just connect the two using wires (same net). However in TI GDE, a wire only connects point-point, so I used a "stereo split mux" to duplicate the LP signal and then tied the unused mux input to "0" using the coefficient "C" block.

Did you get the base files from Allo? or do you need them?
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Old 7th October 2017, 07:53 PM   #23
designmule is offline designmule  United States
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Oh, I see (sort of). Thanks for the explanation. I have not received the files from Allo but following your diagrams, I think I have it pretty much setup. It makes sense once you know where to start. I have one flow which combines the subs, applies EQ, and the lowpass crossover. I have a second flow which does pretty much the same for the mains, in stereo though. The only part I'm struggling with now is figuring out how to add delay to the mains for integration with the sub. Is that anything you messed with?
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Old 7th October 2017, 08:15 PM   #24
DonVK is offline DonVK  Canada
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Not yet, but I can see the value in timing alignment.

I think you want [Basic DSP]->[Delay] or [Basic DSP]->[PacDec Delay] then use properties (right click on instance) to set the #clks delay that you want for a particular output
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Old 7th October 2017, 08:25 PM   #25
designmule is offline designmule  United States
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I think you are right, I just don't understand the units in the components. The help manual indicates the the number entered integer, 1-16 the number of samples the the input is delayed by by I don't know how that correlates to miliseconds. Pac_Dec_Delay makes even less sense to me.
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Old 7th October 2017, 08:34 PM   #26
DonVK is offline DonVK  Canada
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Yes, that one is hard to find.

At the top of the GDE select [View] -> [Properties Window] then set the clock rate you want to "true". Typically its set to 44.1Khz, or 48KHz. It's the base freq. So when you 8x interpolate sample an output its based on this rate, and for delays this is the clock period.
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Old 7th October 2017, 08:55 PM   #27
designmule is offline designmule  United States
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It seems like you would have to have a unique delay for every sample rate supported by the DAC. I'm assuming you set all of the supported rates to True. Or does the delay use the Current Rate? Sorry to waste your Saturday. I do appreciate all your help. Matt
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Old 7th October 2017, 09:24 PM   #28
DonVK is offline DonVK  Canada
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No problem, happy to help. I've been the recipient of tons of assistance from people on this site so I'm good with returning it.

That is another hard one to find one. The GDE uses "configurations" so you can generate a family of design files from a given base design. Each configuration is usually due to a clock rate difference. When you compile the design, all configurations are generated as well. So you get a set of output files. This is how Allo generates a design file for each sample frequency you pick in Volumio2.
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Old 7th October 2017, 10:43 PM   #29
designmule is offline designmule  United States
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I'm trying to wrap my head around the idea of delay as samples rather than time. I think I've got it. If I want 8.25ms of delay and my sample rate is 44,100Hz the math looks like this: .00825/(1/44,000) and I need to delay by 364 samples (actual result is 363.825). Is that right? And based on the number of samples I need to delay by I'll probably need to use Pac_Dec_Delay.
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Old 8th October 2017, 01:07 AM   #30
DonVK is offline DonVK  Canada
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Your math is correct, and the Pac_Dec_Delay is right. You can adjust the 300 output to 364. I have not used this block yet, but that looks right.
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