ADAU1761 LEVEL DETECTOR

Hi Stefano,

I've written a thread about this same topic here: Monitoring average and instantaneous signal levels

The trick is to not use the level detector cell, but instead use the "DSP Readback" cell.

Please let me know if anything is unclear.

Dear BrettG,

thanks for your answer.

I found the way to read the value from the level detector, explained below.

You suggest me a different approach to the problem.

In you opinion, are there any problem using the level detect block?

using the evalboard to sniffing the I2C communication I saw that the readback address

for the level detector is the last one in the module LEVEL DETECTOR define block.

For instance in the previous post i used a "Single Level Detector" and the readback address to use

to read the 4 bytes is:

#define MOD_LEVELCH1_ALG0_SINBANLEVDETS2001_ADDR 194

In a similar way I test the Pass thru Level detector and the readback address is always the last one in the

define block.

Ok,

Thanks for the answer. I'll modify my project as you suggest me!

Last question.

I saw in your example that the numeric format is 5.19. The bits are right bit alligned, do you confirm?

Hi Stefano,

There are a few disadvantages to using the level detector cell when compared to the relative advantages of the DSP readback cell.

(1) The level detector cell is very resource-intensive and it uses more program instructions than the DSP readback cell.

(2) The detection scheme in the level detector is fixed. With the DSP readback cell, you have the flexibility to implement peak, RMS, MS, or whatever kind of detection you want from the blocks available in the SigmaStudio library. Hold, decay, and time constants are also flexible with the DSP readback cell, whereas they are fixed in the level detector cell.

(3) The DSP readback cell can also read back sample-accurate signal levels with no peak/rms/hold/decay, which would give you the true, instantaneous level of the signal in the core. The level detector cannot do this.

(4) Using filters with the DSP readback cell, you can bandlimit or shape the detection signal. In the level detector cells, your options are more limited.

So, there's nothing fundamentally wrong with using the level detector cell, but since it was created for quick, visual debugging and not production system use, it's not very flexible. The DSP readback cell will get you the same or better results.

That is actually a hardware limitation of the ADAU1701, which only has 24 bits in its read-back register.

Since you're using the ADAU1761, which does not have this limitation, you can read back the full 28 bits.

A more detailed description is here:

What are the number formats for SigmaDSP?