[AudioI] Toslink input

[Matt]

On 25/7/20 9:28 am, Peter Heydenrych via People wrote:
> Hi Matt,
> My specific application (speaker crossover) is to take a digital 
> stereo signal from a Toslink source, then apply software filtering in 
> the Pi to output to two 4-way speakers (each speaker has a Tweeter, 
> Midrange, Woofer and Subwoofer, each powered by its own amp).
>
> Your "multiple Pi" architecture can do this but would be hardware 
> heavy. How big an issue is channel swapping?
>

The channel swapping issue has been reported solved when using jackd, 
check here :
https://github.com/Audio-Injector/Octo/issues/1#issuecomment-455135061

I also have a software method for determining input channel alignment in 
the process method here :

https://github.com/flatmax/gtkiostream/blob/master/test/ALSAFullDuplexMinScan.C#L40


I would like to hear from people about whether the input channel 
alignment method can help to align output channels. I assume it will, 
however haven't spent the time testing and observing.


Matt


> Peter
>
> On Fri, 24 Jul 2020, at 09:06, Matt via People wrote:
>>
>> There are a few different approaches to multichannel output.
>>
>> One approach is the Octo sound card with 8 outputs and 6 inputs. The 
>> inputs can be time aligned in software to ensure that no channel 
>> swapping occurs. It is assume this approach can also then be used to 
>> ensure the outputs don't have channel swapping either. Some people 
>> have reported methods to ensure there is no output channel swapping 
>> based on using a jackd subsystem at startup and never stopping it.
>>
>> Another approach is to use one Pi as the I2S bus owner - doing all of 
>> the clocking. Then you can have one Pi per TDM slot. For example, the 
>> one sound card can dump I2S input which all Pi can read. Each Pi can 
>> then do the processing and do stereo output.
>>
>> Matt
>>
>> On 24/7/20 10:49 am, Peter Heydenrych via People wrote:
>>> Not really...I am trying to build a more flexible version of the 
>>> obsolete MiniDSP OpenDRC-DA8, but with optical input, balanced 
>>> output and more flexible processor. With a Pi 4 and Ultra 2 I am 
>>> almost there...
>>>
>>> Peter Heydenrych
>>> peter at heydenrych.net <mailto:peter at heydenrych.net>
>>>
>>>
>>>
>>> On Fri, 24 Jul 2020, at 08:13, Matt via People wrote:
>>>>
>>>> Perhaps we should do a digital input + analogue output board.
>>>>
>>>> To do digital input properly it needs a software interface. The 
>>>> board is meant to tell the software what the incoming sample rate is.
>>>>
>>>> Do you have any ideas around that ?
>>>>
>>>> Matt
>>>>
>>>> On 24/7/20 9:20 am, Peter Heydenrych via People wrote:
>>>>> I'd love to use the 8 balanced outputs of the Ultra 2 - just need 
>>>>> an optical input instead of the analogs...
>>>>>
>>>>> Peter
>>>>>
>>>>> On Fri, 24 Jul 2020, at 07:18, Matt via People wrote:
>>>>>>
>>>>>> To add a toslink input, it would need to operate the I2S clocks - 
>>>>>> that would require a different hardware topology to the current 
>>>>>> devices.
>>>>>>
>>>>>> I think we should do a new product based on this concept. Would 
>>>>>> you be using outputs ? If so what type of output would you want ?
>>>>>>
>>>>>> Matt
>>>>>>
>>>>>> On 24/7/20 8:40 am, Peter Heydenrych via People wrote:
>>>>>>> Thanks for the quick reply, Matt. Would it be possible to add 
>>>>>>> another device to bring in a Toslink signal? Do you know of 
>>>>>>> anything that would be compatible?
>>>>>>>
>>>>>>> Peter
>>>>>>>
>>>>>>>
>>>>>>> On Fri, 24 Jul 2020, at 06:37, Matt via People wrote:
>>>>>>>>
>>>>>>>> Hey Peter,
>>>>>>>>
>>>>>>>> I would love to be able to do this, however that tollink 
>>>>>>>> connector is driven by the codec. They do the I2S to S/PDIF 
>>>>>>>> conversion on chip. S/PDIF receiving is more complex then 
>>>>>>>> sending because we also need to interrupt the operating system 
>>>>>>>> to notify it of a sample rate change.
>>>>>>>>
>>>>>>>> Perhaps it is a good idea to do a future project with the 
>>>>>>>> S/PDIF injection capability.
>>>>>>>>
>>>>>>>> Matt
>>>>>>>>
>>>>>>>> On 24/7/20 8:27 am, Peter Heydenrych via People wrote:
>>>>>>>>> Hi all,
>>>>>>>>>
>>>>>>>>> I have just ordered an Ultra 2 but now see the Toslink option 
>>>>>>>>> is an output.
>>>>>>>>> Is there any possible way to add a Toslink input to a Pi + 
>>>>>>>>> Ultra 2 system?
>>>>>>>>> I'd prefer it if the Toslink output could be converted to an 
>>>>>>>>> input, but adding another module to the system would be 
>>>>>>>>> acceptable.
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>>
>>>>>>>>> Peter
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
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>>>>>>>>
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