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Teensy Audio Bridge for I2C/I2S lines
Teensy Audio Bridge for I2C/I2S lines
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Old 12th July 2018, 01:33 PM   #1
JayShoe is offline JayShoe  United States
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Teensy Audio Bridge for I2C/I2S lines
Default Teensy Audio Bridge for I2C/I2S lines

Hello,

I'm working on a digital audio mixer for pro live mixing. I've been researching this for years but recently stumbled on the Teensy 3.6. It has a very nice library for creating an audio flow using a GUI and Arduino code. Check out the Teensy Audio Library here.

My first test was using the Audio Shield and it succeeded at proving that it is capable of doing what I needed, but the quality was pretty bad. So I purchased some cheap modules off ebay. They are a PCM5102A and a PCM1808. I successfully connected them to the Teensy. They worked great and the sound was much better.

Next, I plan on integrating some even better IC's for my project but before I do I was thinking about creating some type of audio bridge for the Teensy. This would make it easier for me to modularize my project and focus on the individual components rather than a full blown board. The plan is to hopefully get some community support. I've outlined the concept on my post about my project on the teensy forum. Check it out and let me know your thoughts. I'm seeking just an overall concept confirmation and maybe some advice on what features should and shouldn't be included on it.

Here is the link to my project and some more information about this potential bridge.
Teensy with PCM5102a Module via I2S

Click the image to open in full size.
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Old 18th July 2018, 08:31 AM   #2
tataylino is offline tataylino  Philippines
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Great project! I am also researching about digital audio mixer recently and I also came across to this teensy. The only problem is that I can only see pin i2s0_rxd0 and i2s0_rxd1 on its datasheet. This means that it only has 2 I2S channels which means you are only limited to 4 channels. Though I haven't dig deeper into this yet.

Have you succeeded in connecting 4 ADCs in this project? I am excited for this one.
For now I am looking into ADAU1701 for my project. But if you succeed in connecting 4 ADCs to teensy 3.6, I might consider this for my project.
Digital Audio Mixer Project with ADAU1701 – tataylino.com
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Old 18th July 2018, 01:51 PM   #3
JayShoe is offline JayShoe  United States
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Teensy Audio Bridge for I2C/I2S lines
Hello tataylino,

I actually reached out to you on your site once when I came across your project. We are going down the exact same path.

I haven't succeeded at connecting 4 ADCs yet, but I know it's possible and proven because the Teensy Audio Shield has it working with 2 shields and a Teensy.

I'm currently contracting Freelancers to begin development of my audio modules. These modules could technically be connected to whatever MCU I decide works. I just want a working mixer. I really don't care which MCU. :-)

Maybe we can collaborate on this.

Jay
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Old 19th July 2018, 12:58 AM   #4
tataylino is offline tataylino  Philippines
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Hello, Good to meet you again! I was a bit busy and haven't have time to start this project yet. But I really wanted this project done. As of now I am spending little time doing research on this project. I quit on the idea of using XMOS because of its availability here and the development board is too expensive. Based on my research, most known digital mixers uses sharc dsp from analog. This is the best solution but the development board is too expensive and there very few resources on the internet about tutorials. I haven't used one on any of my projects. The cheapest and easiest solution I know for now is the ADAU1701.
I have no doubt you can connect 2 ADCs on teensy and I hope you can connect 4 because that would be perfect for this project because the software library are already there and is easy to use. But I can only see 2 I2S on its datasheet.

I found some STM32 MCU that has up to 5 i2s channels which would be perfect. That would mean up to 10 inputs and outputs. But the only problem is that it only runs at 100MHz so I am not sure if that's enough. The presonus 16.4.2 mixer uses a sharc DSP that runs at around 400MHz. But maybe it is ok for basic mixer function with some EQ function.

Maybe we can collaborate on this project.

Edit:
Yeah, I was right on the I2S channels, teensy 3.6 only have 2 I2S channels.
Why Teensy 3.5 or 3.6
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Last edited by tataylino; 19th July 2018 at 01:20 AM. Reason: added info
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Old 19th July 2018, 01:52 AM   #5
JayShoe is offline JayShoe  United States
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Teensy Audio Bridge for I2C/I2S lines
Remember 2 x I2S lines should be 8 inputs and 8 outputs using TDM right? If we had 4 I2S lines we could have 16x16, right? (EDIT: I don't know)

XMOS = Too expensive. Nobody wants to code for it. But it is surely a rock solid platform and I'd love to have a bridge for it. No GUI..... :-/ Here is a link to the forum post I made about this on XMOS forum.

ADAU = SigmaStudio is good. We need a "I2C/I2S Bridge" for it to make it easier. Why didn't FreeDSP just make a bridge. The PiZero seems to be on hold/pause. Maybe we should make a FreeDSP bridge with no codecs or adc/dac. Just I2C/I2S ports...

Teensy = Working for me so far. Going to create two modules (ADC/DAC) and see how many we can connect and make work. They have a TDM example with 16 channels on each i2S channel. Yes I think the software is coded for two I2S channels. However, I counted more when I looked at the pins....

STM32 = AudioWeaver Free Edition is limited but it is a GUI. Maybe if we made a bridge we could "group buy" a license for the Standard Edition and get all functionality. Great Development modules such as Nucleo-F767ZI... I think this one could work too.

Any others I forgot? I'm pretty sure most "PRO" mixers are using XMOS+Sharc. Currently I'll be going down the path of Teensy, but I'm wide open to suggestions.

I attached a pin assignment that I'm working on. There are a bunch of TX/RX lines - am I missing something?

And TDM in the Audio Development Tool is also attached.
Attached Images
File Type: jpg teensy3.6_pin_assignments.jpg (64.2 KB, 49 views)
File Type: png teensy-tdm.png (243.4 KB, 48 views)

Last edited by JayShoe; 19th July 2018 at 02:14 AM.
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Old 19th July 2018, 01:58 AM   #6
JayShoe is offline JayShoe  United States
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Teensy Audio Bridge for I2C/I2S lines
PS - Danville Signal solutions (XMOS + SHARC)
dspblok 21489uac2 USB Audio Class 2 DSP Module | dspblok | Products
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Old 19th July 2018, 02:14 AM   #7
tataylino is offline tataylino  Philippines
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1 I2s channel can hold 2 inputs and 2 outputs. So if you have 2 I2S channels then that would be a total of 4 inputs and 4 outputs.
TDM is different. Great find! maybe that's a better option!
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Old 19th July 2018, 02:26 AM   #8
JayShoe is offline JayShoe  United States
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Teensy Audio Bridge for I2C/I2S lines
Yes the TDM is exemplified on this board:
OSH Park ~

And I believe it was based on this project on the forum.
Quad channel output on Teensy 3.6 - Page 2
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Old 19th July 2018, 02:58 AM   #9
tataylino is offline tataylino  Philippines
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It looks like you have done tons of research more than I did. That's great! I think the best option now is that board. Unfortunately I can't see any TDM codec IC that have more than 6 input channels. If teensy could handle 2 CS42448 simultaneously, that would be awesome! that would mean 12 inputs and 16 outputs.
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Old 19th July 2018, 03:36 AM   #10
JayShoe is offline JayShoe  United States
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Teensy Audio Bridge for I2C/I2S lines
I don't want to use the CS42448. I'm looking at other modules. Maybe I'll post some more information as I move along.

Are you interested in this project personally or commercially? I admit, I have a small commercial interest in mind selling some boards maybe.
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