Is it possible to use I2S in and out to bypass the codec limitation restricting ADAU1452 eval board limiting audio 48Khz ?
I think you can make it work. Like I said, use ribbon cable with grounds on every other wire. Then make sure to increase the drive strength to max for all the clock and serial data lines.
I2S is a specific format where TDM can be many different formats. So you can think of I2S as a specific implementation of TDM where the LRCLK is 50/50 duty cycle, two channels, 32 bit clocks per channel, a delay of 1 bit clock from the LRCLK edge, Left Justified. The left channel is with the LRCLK low, and the bit clock is falling at the LRCLK edge with the receiver sampling on the rising edge. With TDM you can run it with many different settings but I2S is very specific.
I would start with 48kHz to check all your settings and connections. Then ramp up to 96kHz and then 192kHz. This will help prevent you from pulling out too much hair!
When using an I2S input or output from the ADAU1452, you can use 192kHz with no problems. The issue with using a rate other than 48kHz arises if you wish to use the onboard AD1938 codecs, which are configured for either 44.1kHz or 48kHz. Using a different sample rate for those outputs can cause the codecs not to work correctly. However, for all of the other serial ports, feel free to use any sample rate. If all you're doing is I2S in and out, you don't need to worry about this restriction at all.
Thanks Taylor. How many filter taps are possible at 192 KHz ?
If the core was doing nothing else but processing an FIR filter then it could process approximately 6,000 tap FIR filter at 192kHz fs. If you use IIR filters then it could process around 768 IIR Biquad filters. These numbers will go down based on how much other processing you are doing.
A quick comment about Tyler's post, The AD1938 codec is capable of running at 192kHz but on this simple evaluation board we are running it in standalone mode and you cannot directly communicate with the part to change the settings. So on this eval board it can only run at 48kHz fs.
how many channels are possible using I2s in and out , for this eval board?
This eval board was not built to easily interface all the serial ports. It was designed for low cost. We originally planned to have a more comprehensive and flexible eval board but it was never completed.
So to answer your questions...
You can get to all the ports but it will require some soldering of wires or the use of clip-leads.
All four serial output ports are connected to the codec. So you will need to connect to the test points that are located just above the codec and below the DSP. The codec DAC ports are set to slave so they can remain connected.
There are only two input ports connected to the codec. That would be in_0 and In_1. The codec ADC ports are also set to slave so the clocks are not a problem but the serial data ports are a problem because the codec is driving those lines. So R8 and R9 will need to be removed to disconnect the ADC serial data out of the codec. Then you can use the test points to inject serial data into the evaluation board. The resistors are located between the codec and the test points.
Serial input ports In_2 and In_3 appear on headers and can be easily used.
For both the input and output serial ports:
Serial ports 0 and 1 can run up to TDM16
Serial ports 2 and 3 can run up to TDM8.
So you can get 48 channels in and out of the serial ports.
That said, I know you will have difficulty getting TDM16 to work using jumper wires to another PCB. I have done it but it is always a bit on the edge due to poor signal integrity. You can increase the drive strength and use short jumpers and also run ground adjacent to the clock and data lines. Preferably a ribbon cable where every other conductor is a ground.
thanks for this detailed reply.
what is the longest length you recommend for Jumpers without losing integrity of signal.
I would say my use is limited to 2-4 channels ,so TDM 4 will be enough for me ,I guess ?
The jumper cable limitation is only applicable to TDM 16?
Also will this limitation of length be applicable for non TDM ,2 channel I2S?
It is applicable to all I2S and TDM formats. When the sampling rates go up, and/or the number of channels go up, then it becomes more difficult to run longer distances. You ask how long? Anything more than about 10cm will start showing problems at the higher frequencies. It helps to run a ground wire along with the signals. The best way to do that is to use a ribbon cable with ground on every other wire. This provides an impedance for the signals and a path for the return currents.
So with a ground for every signal you can probably go about 30cm and still be able to run TDM4 at 96kHz. At 192kHz fs may be difficult. Remember that you do have the drive strength control if the ADAU1452 is the master.
Thanks Dave for the extremely fast response!
so the way I am using the board is to provide two channel I2s input and obtain two ways I2s channels after low pass filter.
Dave this might be a silly question to ask , but TDM applies to multichannel I2S only right?
for my application the I2s input are full duty cycle I2S ,from a USB to I2S converter .
After the low pass filtering the I2s out will go to two DACs for upper and lower bands each.
The I2S jumpers will be less than 10cm in any direction. Will this be a practical option for 192 KHz I2S audio.
How many FIR filter taps are needed for making one linear phase filter for two way cross over , at 24 Bit 192 KHz audio ?
The filter will be used in a two way speaker system for separating 200Hz and above ?
is it something ADAU 1452 can do without draining the processing power to its limit for two channel audio?
There are so many options for filter designs so it is hard for me to say. I would expect you could build a filter in the hundreds of taps that may work well enough for you. I would certainly think 2k taps would do it and that leaves plenty of instructions. So I would suggest you obtain some filter design software and see what you can build. Then you will know what you need.
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