Adding post-DSP SPDIF outputs to AVRs

[Martin Parasound]

As you can see everything is separate in my decoder is in the blue part the DTS decoding. This is a other version the PDD1500 I have a special edition limited on 100 pieces with 20 bit DTS decoding. Red is the Zoran 20bit Dolby Digital decoder and yellow the da converters.

 

[Zooqu1ko]

As you can see everything is separate in my decoder is in the blue part the DTS decoding. This is a other version the PDD1500 I have a special edition limited on 100 pieces with 20 bit DTS decoding. Red is the Zoran 20bit Dolby Digital decoder and yellow the da converters.

So, does anything at all in there speak I²S? Why the craptastic resolution of that image?

 

[Taso]

Hi, I did the job. Now I have the digital output for the front L and R channels on my denon x3600h (akm 4458 dac)
But i have a problem. I realized that when Audyssey sends the sweeps from the various channels, as far as the digital output is concerned, I find that when it sends the sweep on the left channel I don't hear anything, when it sends it from the right channel I hear it on both channels, i.e. front R and L.
How can this be? The digital signal is unique and contains both channels. Is absurd.
I connected a frequency generator to an analog input on the Denon... and it's actually the same.
The Denon outputs "dual mono" from the digital output. Do you have any idea?
I do not!

many thanks

 

[voodooless]

It will probably mute the signal as needed via the volume control chips.

 

[eeMGee]

Hi, I did the job. Now I have the digital output for the front L and R channels on my denon x3600h (akm 4458 dac)
But i have a problem. I realized that when Audyssey sends the sweeps from the various channels, as far as the digital output is concerned, I find that when it sends the sweep on the left channel I don't hear anything, when it sends it from the right channel I hear it on both channels, i.e. front R and L.
How can this be? The digital signal is unique and contains both channels. Is absurd.
I connected a frequency generator to an analog input on the Denon... and it's actually the same.
The Denon outputs "dual mono" from the digital output. Do you have any idea?
I do not!

many thanks

I would check the audio interface formats (and MCLK frequency) - they should be the same (see data sheets of the AK4458 and WM8805 and check the appropriate chip pins):

Your board is here:

 

[MCH]

It should be easy to see with a logic analyser if one of the channels is muted in the i2s signal. As you have a few i2s inputs and outputs you might be able to find out where the signal gets lost or mixed.
What I can anticipate to you is that the wm8805 you are using has no capabilities to mix channels. Only has stereo inputs (i2s and spdif) and mux to select which stereo signal to output, that's all.

Edit: but indeed the ak4458 has a mono mode that could do that (page 57 of the datasheet). Are the tones by chance inverted when you hear the tone in both channels?
If that is the culprit, I don't think it has an easy solution.

 

[Taso]

It should be easy to see with a logic analyser if one of the channels is muted in the i2s signal. As you have a few i2s inputs and outputs you might be able to find out where the signal gets lost or mixed.
What I can anticipate to you is that the wm8805 you are using has no capabilities to mix channels. Only has stereo inputs (i2s and spdif) and mux to select which stereo signal to output, that's all.

Edit: but indeed the ak4458 has a mono mode that could do that (page 57 of the datasheet). Are the tones by chance inverted when you hear the tone in both channels?
If that is the culprit, I don't think it has an easy solution.

Thanks for the reply. Do you mean phase inverted? I can try to input, with a frequency generator, a 1khz tone on an RCA input and check with an oscilloscope the output from a DAC connected to the digital output. Is this what you say? thanks

 

[Taso]

It will probably mute the signal as needed via the volume control chips.

I don't quite understand what you're saying. But why do I have the right signal output on both channels? Thank you

 

[Taso]

I would check the audio interface formats (and MCLK frequency) - they should be the same (see data sheets of the AK4458 and WM8805 and check the appropriate chip pins):
View attachment 330553
View attachment 330554

Your board is here:
View attachment 330558

Thanks for the reply, I'll check if the white board has soldered pads, but I don't think so. It's like when I bought it, I didn't solder those pads. Thank you

 

[MCH]

Thanks for the reply. Do you mean phase inverted? I can try to input, with a frequency generator, a 1khz tone on an RCA input and check with an oscilloscope the output from a DAC connected to the digital output. Is this what you say? thanks

Don't worry, it is not relevant.
Reading fast the datasheet of the ak4458 I believe I read that when it outputs one channel in "dual mono", the R and L signals are inverted. I don't have the datasheet in front of me to confirm now.
But you are bypassing the DAC, so shouldn't be the case.
The important thing is that the ak4458 can do channel mixing, and the wm8805 you are using instead cannot, and this could be a possible reason for your observations.

 

[Taso]

Don't worry, it is not relevant.
Reading fast the datasheet of the ak4458 I believe I read that when it outputs one channel in "dual mono", the R and L signals are inverted. I don't have the datasheet in front of me to confirm now.
But you are bypassing the DAC, so shouldn't be the case.
The important thing is that the ak4458 can do channel mixing, and the wm8805 you are using instead cannot, and this could be a possible reason for your observations.

In fact I'm getting the signal before the DAC. I really don't know how to resolve this

 

[voodooless]

I don't quite understand what you're saying. But why do I have the right signal output on both channels? Thank you

The AVR uses volume control chips after the DACs. It could simply mute the channel it doesn't need.

As for mono mode: doesn't this still output the same signal to both channels? Looks like that is configurable. I don't see a real use case for this in the context of an AVR though. Good to check nevertheless.

 

[eeMGee]

Try to check LRCK (fs) signal on yellow wire - should be like on the pic (it is from AVR-X3400H, but I think it is the same as 3600):

Or you can measure frequency of LRCK by multimeter - should be 96 kHz (or 48 kHz), I suppose.

Edit: The best is to measure it on the WM8805 on your board directly - pin 19.

 

[Zooqu1ko]

[...]I realized that when Audyssey sends the sweeps from the various channels, as far as the digital output is concerned, I find that when it sends the sweep on the left channel I don't hear anything, when it sends it from the right channel I hear it on both channels, i.e. front R and L.

Is it correct that your AVR has 2 ak4458 DACs, but less than 16 output channels? In that case it's quite possible that they have tied together 2 output channels at least for L and R for a slight reduction in output noise, although I would have expected that to be highlighted in the technical specs. If you don't have a logic analyzer already, I've had some success with a "cheap" 16 channel 100MHz USB analyzer with Pulseview to decode S/PDIF.

Also, does this only happen with the sweeps, or also when playing back e.g. a CD or other simple PCM audio in "direct" mode without any processing?

 

[Taso]

Is it correct that your AVR has 2 ak4458 DACs, but less than 16 output channels? In that case it's quite possible that they have tied together 2 output channels at least for L and R for a slight reduction in output noise, although I would have expected that to be highlighted in the technical specs. If you don't have a logic analyzer already, I've had some success with a "cheap" 16 channel 100MHz USB analyzer with Pulseview to decode S/PDIF.

Also, does this only happen with the sweeps, or also when playing back e.g. a CD or other simple PCM audio in "direct" mode without any processing?

hi, today I'll do the tests you tell me, I'll come back here. I've attached a block diagram, maybe it'll be useful for something. It's from my AVR, x3600h. Yes my AVR has two AK4458 DACs but less than 16 channels! many thanks

 

[MCH]

Well, you can pick up the two following channels with a second i2s > spdif board and run two external DACs as monoblocks. Isn't it going to be cool? you'll need a preamp though

 

[Taso]

@MCH @Zooqu1ko @eeMGee @voodooless

HI, I did a couple of tests.
First of all I wanted to correct this:
From the implemented digital output (white board, i2s>digit coax), I hear the left channel of the Denon (music and audyssey sweep) on both speakers (passing through an external DAC). No good!
Same thing even with audyssey off, so no environmental correction. I had said that the channel I heard was the right. Mistake! Little difference, the problem is the same!

If I connect the amplifier and speakers to the front preout output... everything is fine (both music and audyssey sweep)... even with the white board (i2s>digit coax) installed and connected (to the input of the AKM Denon) .

I can't have two external DACs with two digital outputs because I need a single digital output (left and right)... to enter a 10x10 miniDSP that I use as an electronic crossover to drive 3-way speakers (3 amplifiers).

What type of logic analyzer could I buy? There is an analog oscilloscope and a digital USB (PC) oscilloscope... but they do not analyze digital signals.

One question: For direct mode just go to the menu and turn off audyssey, correct?

However, I carried out some trivial measurements with a USB oscilloscope / PC. I measured all signals on three different points.
On the connector of the original denon board (where I get the signals from), on the white connector of the white board..and on the pins of the WM8805.
The 3 point signals are always the same, except for the MCK.
MCK on the connector of the original Denon board.. I measure 78Khz/890mv, on the white connector of the white board I measure approximately the same voltage but 87khz, and, on the pin of the WM8805 (pin 20) I measure 34khz/800mv. Maybe this thing isn't important.
Furthermore, on pin 19 of the WM8805 I measure 48Khz (I think this is normal).

many thanks for any help. ....

 

[MCH]

hey Taso, unfortunately i cannot help you as i don't know any IC that can take 4 channels i2s and route 1 channel of each pair to be the L and R channels of a single SPDIF signal. The multichannel ICs that i know that can route incoming i2s signals to SPDIF work always with LR pairs of signals. But i know next to nothing, maybe others can chime in with something.
At this point, seems the origin of the issue is quite clear. You can confirm it if you manage to pick the Right channel from another i2s data line and it behaves the same than the left. I don't think a logic analyzer will tell you anything you don't know yet.

other comments:
your readings of the MCK don't seem right, they should be in the MHz range. Maybe the oscilloscope you are using does not reach to the frequency you want to measure?
The reading on pin 19 of the wm8805 is the LRClK = current sample rate of the i2s signal. that one being 48kHz seems ok.

 

[eeMGee]

@MCH @Zooqu1ko @eeMGee @voodooless

HI, I did a couple of tests.
First of all I wanted to correct this:
From the implemented digital output (white board, i2s>digit coax), I hear the left channel of the Denon (music and audyssey sweep) on both speakers (passing through an external DAC). No good!
Same thing even with audyssey off, so no environmental correction. I had said that the channel I heard was the right. Mistake! Little difference, the problem is the same!

If I connect the amplifier and speakers to the front preout output... everything is fine (both music and audyssey sweep)... even with the white board (i2s>digit coax) installed and connected (to the input of the AKM Denon) .

I can't have two external DACs with two digital outputs because I need a single digital output (left and right)... to enter a 10x10 miniDSP that I use as an electronic crossover to drive 3-way speakers (3 amplifiers).

What type of logic analyzer could I buy? There is an analog oscilloscope and a digital USB (PC) oscilloscope... but they do not analyze digital signals.

One question: For direct mode just go to the menu and turn off audyssey, correct?

However, I carried out some trivial measurements with a USB oscilloscope / PC. I measured all signals on three different points.
On the connector of the original denon board (where I get the signals from), on the white connector of the white board..and on the pins of the WM8805.
The 3 point signals are always the same, except for the MCK.
MCK on the connector of the original Denon board.. I measure 78Khz/890mv, on the white connector of the white board I measure approximately the same voltage but 87khz, and, on the pin of the WM8805 (pin 20) I measure 34khz/800mv. Maybe this thing isn't important.
Furthermore, on pin 19 of the WM8805 I measure 48Khz (I think this is normal).

many thanks for any help. ....

What is your external DAC?
Is it miniDSP? If so, I suggest to check miniDSP settings...

P.S.: MCK is 256xfs - in this case 12,288 MHz (for fs 48 kHz).

 

[voodooless]

I don’t see how an incorrect LR signal would be able to copy the channels… curious