ADAU1701 -- Multiple I2S sources

Hello Carlos,

Yes, there are only one set of clocks and they have to be associated with the serial data that you are using and also the master clock has to changed as well. The master clock most likely needs to be 256 x fs. (it is set with the PLL pins.) I am assuming your sources will have a master clock output.

I would not use a physical switch but there are plenty of multiplexers that can switch between the Master clock, LRCLK, BCLK and SDATA signals. Then you can use a single switch to select the input. If there is logic available you could make it happen automatically. You should mute the output before switching the serial port. The only thing I would worry about is that the PLL really should be shut off when switching the master clock. Do you have a system controller in your system?

What you really need to use is the ADAU1452 that has sample rate converters in the part. That would solve your problems.

Dave T

Thanks Dave,

When you suggest "multiplexers", do you mean functionality inside the 1701, or do you mean external logic components such as the 74x257?

As for the ADAU1452, I've been trying to stick to the 1701 to avoid the extra external DACs (and potentially I will want to take advantage of the input ADCs as well).

Thanks,

Carlos

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Hello Carlos,

Yes, I was talking about external logic components.

I assume you are developing a product? What is the rough prototype/production schedule and what kind of anticipated volumes will there be?

Also what are some of the design constraints? Power? Size? Channel Count? etc?

Dave T

Hello Carlos,

I was just answering a similar question from another user and realize that if you have any filters or oscillators in the system then you will need to change the filter coefficients and program for the new sample rate. So really, to do this you will need an external controller for two reasons. The first is that the only way to restart the PLL is to pull down the reset pin. The second is to load in the new filters etc. So in the end the easiest way to do this will be to have an external controller load in the two different programs and change the master clock source.

Dave T

Thanks again Dave!

My application is a personal hobby / DIY project (with a remote potential to some day becoming a commercial product), which is the main reason why I'm trying to keep it as simple as possible (e.g., the 1452 seems to come only in QFN package --- that's a bit intimidating for me to solder; additional external components, especially external DACs that usually come only in fine-pitch, mean additional soldering headaches; etc.)

An external MCU should not be too bad (something like an 8-pin AVR ATtiny should do the job, right? I've used those in several of my personal/hobby projects).

Your comment brings me to a big revelation --- when recently trying some of the filters, I now (looking at it in retrospect) think I had the incorrect sampling rate in the project.... I thought I was losing my mind (or worse, my hearing!! :-) ) when I was configuring a filter at some given frequency and what my ear was telling me was ridiculously incompatible (but then, for some reason it didn't occur to me to think that the filter was wrong --- I was simply doubting my ear ..... oh well, that was funny.... maybe I am losing my mind, what with not even occurring to me that I should have doubted the filters!! :-) )

Thanks,

Carlos

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