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Compatible DIGI boards for DSP?

Tony Tromp

March 28, 2021 10:30

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Hi guys,

So far I am quiet happy using the DAC+DSP board. As I am having an external DAC (provided by my Active Speakers), I only use the Toslink connections from that board and completely neglect the DAC part in the DAC+DSP board.

As my usecase going to more digital inputs, I am looking for more digital I/O in combination with the Hifiberry DSP. If I add more digital inputs to this board, would these show up as inut devices and handled by the DSP as sound source? Is it possible to get the all-digital boards to work with the newer DSP board?

Kind regards,
Tony

 

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15 comments

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  HiFiBerry team March 29, 2021 07:35

  Unfortunately there is no such board and we don't plan to implement this. As the DSP only offers one SPDIF input, this would require quite a lot of additional circuitry. Therefore, I would recommend a simple external SPDIF switch.

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  Tony Tromp March 29, 2021 08:53

  Thanks, i can make it work with an external switch.

  Would it be possible to use the (1x) input from a Hifiberry Digi+ I/O board=> to the DSP and output => via DIGI2 Pro board?

  Thanks,
  Tony

   

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  HiFiBerry team March 29, 2021 08:54

  No, it's not possible to combine multiple sound cards as the Digi+ I/O and Digi2 Pro.

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  Robin Rainton April 08, 2021 09:25

  I have an interest in the digital I/O capabilities of the DAC+ DSP for the following use case (please forgive if this is off topic, but seems relevant question here):

  We have ceiling speakers in more than 1 room at home (Focal Custom IC 106s driven by SMSL SA-98E amps). They sound pretty good TBH, but the ceiling clearly not being the most ideal place for a speaker, figure these could benefit from some DSP love (please tell me if I'm wrong here!).

  Let's say I install HiFiBerryOS on a Pi4 with a DAC+ DSP and use that as a Spotify Connect endpoint. The analogue outputs of the DAC+ DSP feed into power amp driving speakers in room 'A'.

  One configures some DSP correction for room 'A' and hopefully that will improve the sound.

  Next, say we want to provide similar DSP correction for room 'B'... a second Pi with DAC+ DSP board will be required, right? Unless it's possible to add a further stereo output pair (separately processed channels) to this board... he asked hopefully?

  Say additional outputs cannot be added. OK, add a second Pi/DAC+ DSP combo to replicate the system so far. If done that way, can one feed the digital out (the audio from the planned Spotify endpoint) from the DAC+ DSP driving room 'A' into the digital input of this second DAC+ DSP? Or will that be an already 'corrected' digital signal and therefore have nasty side effects?

  Ie. is the TOSLINK output of a DAC+ DSP the signal after processing or before? Or can it be configured? If this is/can be configured as the pre-DSP signal, please confirm one can connect that as input to a second DAC+ DSP and have it correct using it's own parameters for room 'B' as I'd like?

  If the answer turns out to be, "The TOSLINK output of the DAC+ DSP is the signal after processing and always will be"... any ideas how to get the raw digital output (ie. the unprocessed Spotify output) from room 'A' to room 'B'? Some kind of LAN based stream mirroring? I don't think Spotify Connect has such a feature but does HiFiBerryOS (or any other Linux audio stuff) have any such magic?

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  HiFiBerry team April 08, 2021 09:32

  If you need a system for multiple rooms that you want to control independently, you need multiple Pi(DCA combination - one for each room.
  
  For a multi-room setup with multiple rooms, you should use a central server. As far as I know, there's a Spotify plugin for Logitech Media Server (LMS) that should allow to stream to multiple rooms. Unfortunately Spotify itself doesn't allow multiple parallel players.
  The most advanced software to implement this IMHO is Roon. However, it's not cheap and you would need to use Tidal instead of Spotify. Therefore, LMS is still very popular. Both Roon and Squeezelite (for LMS) are integrated in HiFiBerryOS.

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  Robin Rainton April 08, 2021 09:42

  OK, thanks. Will check out LMS.

  As for the I/O from a DAC+ DSP... can you please confirm the TOSLINK output is always the signal after processing and that can't be changed or configured?

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  HiFiBerry team April 08, 2021 09:50

  The DSP is fully programmable and it can be programmed to whatever you like using Analog's SigmaStudio software.  Filters can be simply changed in HiFiBerryOS, but if you want to implement your own audio routing and/or processing, you can do this using SigmaStudio. However, it's not something for beginners, therefore, we recommend this only to users with some experience in this area.

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  Robin Rainton April 08, 2021 12:20

  "it can be programmed to whatever you like" is a bit of a misleading statement - within the limits of how this board has been designed and the I/O connected of course. Oh, and one's development skills ;)

  On the first point, this means we still need to know (and if this could be explained on the data sheet would be awesome):

  1. Does the DSP see the TOSLINK digital input and the I2S input from the Raspberry Pi as 2 separate inputs?

  2. I notice there's an 'IN2' listed on the DSP I/O header which means (depending on the answer to Q1) there are actually 2 or 3 DSP inputs available - which is it?

  3. The datasheet shows an eDac output and says this is connected to the onboard DAC. Ie. tell the DSP to output to the 'eDac' and that comes out of the analogue outputs, right? But is this what drives the TOSLINK output too or is that connected to a separate DSP output?

  4. Again, from the datasheet there is 'OUT1' and 'OUT2' listed so same as the inputs, depending on if the TOSLINK  output is a separate connection from the 'eDac' there are actually 3 (or 4) outputs available?

  If you could please confirm all this, that would be great.

  Now, call me crazy, but in my use case where I only want one input fed to multiple room correction DSPs... why can't one feed the I2S from a Raspberry Pi into multiple DAC+ DSP boards (each with different correction programming)? In this scenario, what would be needed is a way to multiplex the programming/control - so I have to ask - which pins on the Pi header are used for that? A single Pi with multiple DAC+ DSP boards in a single case could be an awesome solution for multiroom audio, yes?

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  HiFiBerry team April 08, 2021 12:36

  TOSLink and Pi are 2 separate inputs to the DSP and analog and digital out are 2 separate outputs.
  
  there are additional I2S inputs and outputs on the pin header. However, we don't recommend to try to use these if you're not VERY experienced in digital audio. I2S is not something that you can simply connect:
  https://www.hifiberry.com/blog/techtalk-i2s-i2s/

  You can't use multiple DAC+ DSP on the same Pi as the Pi's GPIO system isn't designed as a bus system that can support multiple cards. 

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  Robin Rainton April 08, 2021 12:43

  Excellent. Thank you for clearing up those I/O questions.

  "You can't use multiple DAC+ DSP on the same Pi"... why not (I mean, beyond that I would have to build something to physically allow this)? I was just looking at some of the doco around programming these and says the DSP toolkit uses SPI. SPI multiplexing is a thing, so if that's the programming mechanism seems doable.

  You understand I'm looking for a reason to buy multiple boards from you guys rather than something from a competitor, right? :)

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  HiFiBerry team April 08, 2021 13:04

  Our recommendation is clear: Use one Pi for each DAC+ DSP.
  Sure, you can try to multiplex and do all kind of stuff. There is no documentation for the stuff you're planning to do. However, there is strictly no support from us for this. If you think, a competitor's product works better for you, that's fine. It would be just worse for you and us if I would tell you to try something the product never was designed for. 

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  Robin Rainton April 08, 2021 15:48

  Yeah, I get where you are coming from and that's cool: if a user does something that isn't recommended then no warranty, no support, etc, etc. I'm good with that.

  On the other hand, HiFiBerry are selling bare electronics boards for hobbyists/enthusiasts. Sure, some will just plug them in a Pi and be done, but some (like me) might want to tinker more.

  IMHO, for boards like this think it's appropriate to document every connection to/from the board. I mean, ideally I'd like to see a schematic but that's probably asking too much so I'd at least like to know which of the pins on the GPIO header are actually connected and which component they are connected to.

  FWIW, if I read the specs correctly, a regular Pi can support 2 SPI slaves on SPI0 and 3 on SPI1 (using CS's) and then one could add many more by messing with software and using other GPIOs for CS. That would be plenty for my needs.

  So basically, if you can confirm which pins the DAC+ DSP uses that would be great. I assume it's only I2S for audio data and SPI for control, plus power & ground but can't rely on assumptions. Confirmation of the specifics would be enough for me to give multiple boards a go is all. At my own risk, etc, etc.

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  Robin Rainton April 09, 2021 06:09

  Ahhhh... this almost answers the question:

  https://www.hifiberry.com/docs/hardware/gpio-usage-of-hifiberry-boards/

  "GPIOs 2,3 are used for configuration" - wouldn't mind knowing more about that is all.

  Also, I found on the DAC+ DSP datasheet, "Onboard EEPROM allows to board to boot and run even without the Raspberry Pi" which seems to break the "one Pi for each DAC+ DSP" rule ;) ... but it also implies what I want to do really should be possible :)

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  Jonathan Phillippe April 17, 2021 12:26

  Robin,

    Sounds like what you're after is a multi-room music (MRM) setup which Amazon Alexa supports.  You can download an AVS w/ MRM SDK for a raspberry pi.  There are multiple tutorials out there showing how to do this. 

   

  As for the multiple DAC's of a single I2S stream - many DSP's support a daisy chain mode where a single I2S bus setup in a multi-channel configuration is sent to DSP "A" which processes <insert number> of channels and the remaining channels are sent to DSP "B" for processing and so on...  This requires use of TDM mode and the DSP pins configured correctly on the PCB.  It's not clear to me if the DAC+ is configured in such a way.  The ADAU1451 DSP supports this.

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  Robin Rainton April 17, 2021 15:59

  No Jonathan Phillippe, I don't want anything to do with Amazon Alexa thanks.

  Read what HiFiBerry team says above, "TOSLink and Pi are 2 separate inputs to the DSP and analog and digital out are 2 separate outputs." This implies that one possible solution could be to program the DSP to send the digital input from the Pi directly to the TOSLink output, which could then be fed into a second device. Sounds like it could work but hardly elegant and would not be my preferred solution.