It has been my long desire to design a digital audio mixer but there a too little resources regarding digital signal processing. While researching I stumble upon this little chip from analog which don’t require DSP knowledge. It is program using a software called sigma studio. There is no programming language, you just need to drag and drop modules. I am still on learning process, and this is just a test of what can I able to pack on a cheap ADAU1701 DSP. Considering the price of this DSP and the size of its memory, these modules that I was able to put was amazing.
What I was able to get with the limitation of ADAU1701:
- 8 input channels
- all have 3 parametric equalizer
- all have compressor
- all have volume control
- all have 1 pre aux
- all have 1 post aux
- 4 output channels
- 2 as main output with 6 band equalizer
- 1 as pre Aux output
- 1 as post Aux output
That’s about it. Adding more modules will prompt an error that you are out of memory. Considering what most 8 input analog mixer are offering on the market, this features are better. This project can be further improved so I have uploaded the project file on my download page so you can edit it yourself.
Sigma Studio Project
Main Schematic
Channel strip
These controls can be accessed through a microcontroller connected to it via I2C. The microcontroller can then be connected to user interface such as buttons and displays like LCD.
10 Channel variant
I have tried to use the maximum possible inout of the ADAU1701 which is 10 inputs but simplifying the schematic and removing the compressor on channel 7 and 8. The 2 additional channel can be used for bluetooth audio. I was able to achieve the following:
- 10 input channels
- Channels 1-6 has HPF, 3 band Parametric EQ, Compressor, 2 aux sends
- Channels 7 and 8 has 3 band Parametric EQ and 2 aux sends
- Channel 9 and 10 has 3 band EQ
- 4 output channels
- 2 main out with 10 band graphic EQ
- 1 Pre Aux out
- 1 Post Aux out
I think that is the best I can have for ADAU1701 DSP.
Multi-track Recording
This is the biggest challenge for this project, for now I don’t have any idea on how can it be done and how it can work with the ADAU1701. What’s clear for now is that the ADAU1701 DSP can’t be used for this purpose. I know it can be done using the XMOS chip but the development board is too expensive for me.
Conclusion:
The ADAU1701 is a powerful DSP for audio application. It can surely be used for digital audio mixer application with limited input channels. 8 channels maybe the most channels you can have for this application. You can have as much as 10 total inputs but you need to limit some functions like compressors to be able to use all the 10 inputs or else you will ran out of memory and the project will not compile at all.
Notes:
- ADAU1701 only have 2 ADC channels build in, you need an external ADC to be able to add 6 more inputs.
I have yet to build the actual hardware but I am not sure when I can do it. When I got the fund and time for sure but I am not sure when.
Downloads: