Stable SPDIF I/O at 44.1kHz on EVAL-ADAU1452MINIZ EVM?
I am measuring the SPDIF I/O performance of the ADAU1452MINIZ EVM. My measurement system can record the exact output (with delay) when using SPDIF loopback at 44.1 and 48kHz. I set up the EVM (with SigmaStudio) to use SPDIF TX and RX with simple I/O as described in the user guide. When I set the sampling frequency to 44.1kHz I find that my recorded output from the EVM given a one sample pulse train input (repeats every 500ms) is smeared in time and the peak amplitude varies. (Note that my audio device, an M-Audio ProFire 2626, cannot sync lock to the SPDIF TX at 44.1kHz but can lock at 48kHz.) With the sampling frequency at 48kHz and the EVM the master Fs clock, the recorded output of the impulse train is still smeared by 62 samples, but the peak and smeared samples are always the same. I assume the smearing is due to the ASRC doing its job. Is there a way to get similar stable performance with the EVM at 44.1kHz?
Audio Signal Processors
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SigmaDSP Audio Processors
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Hi DMR,
Yes, the smearing effect is indeed due to the ASRCs doing their job. There is some filtering going on during resampling, so you'll never really get an output that looks the same as the input. However, listening to real music going through an ASRC should sound the same on the way out as on the way going in. You'll only notice the effect of the ASRC if you start looking at individual samples.
So, I have one initial thought here. I'm wondering how you're setting the system to run at 44.1 kHz. Note that the crystal on the EVM is 12.288 MHz, which is set up by default to go into clock generator 1 and produce the proper clocks for a 48 kHz audio sample rate. That's the default clock for the DSP core, and the S/PDIF transmitter as well.
In order to run the DSP and S/PDIF transmitter at 44.1 kHz, you actually have to reconfigure clock generator 1. Otherwise, the system will always run at 48 kHz. You can find the clock gen 1 M and N settings on the CLOCK_CONTROL tab in SigmaStudio's register configuration GUI.
Figure 18 in the datasheet shows that the magic numbers for generating 44.1 kHz from a 12.288 MHz master clock are N=49 and M=320. So, I'd suggest setting up clock generator 1 to do that.
I haven't actually tried this, but I think it will work. Anyway, give it a try. If it doesn't work, I'll get out my eval board and try it myself!
Thanks for the advice. I am new to SigmaStudio and was not aware what needed to be set manually and what is handled automatically. Your suggestion worked; I can now sync to the EVM spdif output at 44.1kHz. FYI, I get the same net delay (~1 ms) with either sample rate and also the same decimation/interpolation filter response (within 10^-3 max.) of 62 samples.
Thanks again Yagami. I have a related question. From reading the EVAL-ADAU1452MINIZ EVM User Guide it appears that the system supports fs=44.1kHz and 48kHz using the audio codec. I assume the default is 48kHz based on the previous discussion. How do I change the settings in SigmaStudio for fs=44.1kHz for the audio codec on the EVM? The user guide and SigmaStudio help to do not explain how to do this. I tried changing the clock generator like I did for SPDIF 44.1kHz but I lost all output when doing so.
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