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Old 30th July 2017, 08:59 PM   #21
DPH is offline DPH  United States
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-90 on the third isn't too bad for the integrated.

Anyone done multichannel on this guy yet? I haven't dug into the documentation to see if we can slave 6 channels on to the GPIO/I2S or if it has to be done via USB.
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Old 30th July 2017, 09:19 PM   #22
Zootalaws is offline Zootalaws  New Zealand
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Quote:
Originally Posted by DPH View Post
-90 on the third isn't too bad for the integrated.

Anyone done multichannel on this guy yet? I haven't dug into the documentation to see if we can slave 6 channels on to the GPIO/I2S or if it has to be done via USB.
The Allo Piano 2.1 has two i2s-capable DAC chips driving four channels -2 left, 2 right. No idea how they are managing that, whether both DACs are receiving the same stream or whether all four channels are on separate serial streams.
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Old 30th July 2017, 09:22 PM   #23
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by DPH View Post
-90 on the third isn't too bad for the integrated.

Anyone done multichannel on this guy yet? I haven't dug into the documentation to see if we can slave 6 channels on to the GPIO/I2S or if it has to be done via USB.
Not sure where you are getting your numbers, but the 3rd order distortion for the integrated sound codec on the Tinker board was 0.0223% in my measurement, which translates to -73dB with respect to the fundamental. Also the total noise floor is only down 73dB below the fundamental level (0.0483%-0.0250%=0.0233%, or -72.65dB). These number are pretty crappy for a DAC. OK for casual headphone listening perhaps.

In the other plot, presented as a comparison, the 3rd order distortion of an inexpensive ES9023 USB dongle was -107dB (0.0004%) and the total noise was about -85dB below (0.0055%). Also, the maximum output level is higher by over 10dB, meaning it can drive amps with over 1V input sensitivity. All in all this is a good DAC for the price (which was way under $50 for a populated PCB).
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Old 30th July 2017, 10:14 PM   #24
DPH is offline DPH  United States
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Charlie -- I mistakenly didn't see that your primary harmonic wasn't at 0 dB.

Zoot -- thanks for the info! At least someone's out there doing it in some capacity. I'll have to take a closer look at what IO is available.
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Old 31st July 2017, 04:46 AM   #25
CharlieLaub is offline CharlieLaub  United States
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Charlie -- I mistakenly didn't see that your primary harmonic wasn't at 0 dB.
Ah, that makes sense now. The software uses the max input level of the ADC as 0dB. I wish I could scale the data so that the fundamental is always at 0dB to avoid exactly this type of confusion, but I can't seem to find out how to do it (it's REW v5).
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Old 31st July 2017, 05:48 AM   #26
DPH is offline DPH  United States
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All good. And usually I distrust the %age numbers as they can be easily monkeyed with depending on bin width.

In searching around, looks like there's only one stereo I2S arrangement. Not sure if some of the other pins can be thus reconfigured. Might make more sense/simpler to pipe it all through USB.
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Old 1st August 2017, 03:46 PM   #27
Jerms is offline Jerms  United Kingdom
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Originally Posted by Zootalaws View Post
The Allo Piano 2.1 has two i2s-capable DAC chips driving four channels -2 left, 2 right. No idea how they are managing that, whether both DACs are receiving the same stream or whether all four channels are on separate serial streams.
From what I gathered whilst mooting 2xPlainAMP etc a year or so ago....

I2S on the Pi is 2 channel output.
It is possible to I2C address DACs or AMPs via bus address (0/1 that I know of) to program/load different DSP into each DAC/DSP/AMP.
PlainAMP had a jumper to select bus address if running two in parallel. I guess Piano 2.1 has it controlled on the board.

So each DAC gets the whole stereo signal sent to it. The DSP decides what to do with it after that.

J.
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Old 1st August 2017, 04:24 PM   #28
CharlieLaub is offline CharlieLaub  United States
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I2S is not, as you say, "2 channel". I2S is a hardware communication bus. What data you send over that hardware is determined by the software interacting with the I2S bus on either "end". You can send and receive lots of audio channels if you want - just check out the "Octo Pi soundcard" from Audio Injector for an example.
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Old 1st August 2017, 05:53 PM   #29
DPH is offline DPH  United States
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The point being made is that we have this lovely microcontroller already, and you have to figure out a means of breaking up a 8-channels I2S stream into 4 stereo I2S streams to interface with at least any of TI's, Cirrus's, or AKM's DACs (I just checked DS's). It'd be nice to not have to use another layer of glue to get the job done.
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Old 2nd August 2017, 12:39 PM   #30
Jerms is offline Jerms  United Kingdom
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Originally Posted by CharlieLaub View Post
I2S is not, as you say, "2 channel". I2S is a hardware communication bus. What data you send over that hardware is determined by the software interacting with the I2S bus on either "end". You can send and receive lots of audio channels if you want - just check out the "Octo Pi soundcard" from Audio Injector for an example.
Ah, not so much of a hardware or microcode limitation then.... More of an OS or driver thing if there's a limit anywhere?
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