Adding post-DSP SPDIF outputs to AVRs

[Zooqu1ko]

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

The block diagram would indicate that the PCMF signal should carry (both front) left and right signals. The channel that's has no output connected is apparently RSV (reserved). You appear to have the full service manual - is there any indication which analog outputs of the DAC are wired to L and R, and which one is skipped?

[...]
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.

Assuming you're not dealing with sample rates > 48kHz while debugging, any logic analyzer supported by sigrok with >= 100MHz sampling rate should be OK. I'm using one of the cheap clones you can find e.g. on ebay if you search for "Mini 16 Logic Analyzer USB 100M". The software I'm using is of course PulseView, which has decoders for I2S and S/PDIF.

 

[Taso]

Qual è il tuo DAC esterno?
È miniDSP? In tal caso, suggerisco di controllare le impostazioni del miniDSP...

P.S.: MCK è 256xfs - in questo caso 12.288 MHz (per fs 48 kHz).

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).

hi, thanks for the reply. minidsp is set up well. I also tried with another DAC (audiolab m-dac plus)...same behavior.
I wonder where the missing channel went!
Do you think I need to solder or desolder some pads on the white board? I'm almost desperate!

Digitale Interface I2S vers SPDIF BNC WM8805 24bit 192kHz - Audiophonics

This digital interface allows you to input a DATA I2S signal with MCLK and convert it to SPDIF 75 ohm.

www.audiophonics.fr

many thanks

 

[MCH]

I wonder where the missing channel went!

Wm8805 is very forgiving. What I would do is to desolder the data cable (the red one) on the AVR side, play something on the right channel only, and with the red cable, touch on the different suspicious pads (the ones named DACPCMxxxx) until you have sound out of the wm8805.
But finding where the R channel is will not solve your problem, you still need to find the hardware that allows you to bring the two channels to one single spdif signal. Nobody has yet suggested something that could do that. I can't think on anything but a computer or a microcontroller or something like that.

 

[Taso]

Wm8805 is very forgiving. What I would do is to desolder the data cable (the red one) on the AVR side, play something on the right channel only, and with the red cable, touch on the different suspicious pads (the ones named DACPCMxxxx) until you have sound out of the wm8805.
But finding where the R channel is will not solve your problem, you still need to find the hardware that allows you to bring the two channels to one single spdif signal. Nobody has yet suggested something that could do that. I can't think on anything but a computer or a microcontroller or something like that.

Excuse me for a question. But does the L and R signal go through the red wire (data) or the yellow wire (LRCK)? Thank you

 

[Taso]

@Weeb Labs
Hi, couldn't you help me? Thank you, you would be very kind.

 

[MCH]

Excuse me for a question. But does the L and R signal go through the red wire (data) or the yellow wire (LRCK)? Thank you

The data line (red cable in your pictures) carries the audio data for both channels.

The LRCK wire carries a clock signal so that the receiver knows what is the data for the left channel and the right channel. No audio information in this signal.

But don't get confused: yes, your red cable carries two channels, but from your explanations it seems that it carries two copies of the left channel signal, what is perfectly feasible.

 

[Zooqu1ko]

Excuse me for a question. But does the L and R signal go through the red wire (data) or the yellow wire (LRCK)? Thank you

I²S - Wikipedia

en.wikipedia.org

 

[Taso]

friendsssssssss!!!! I solved! everything works perfectly! yuhuuuuuuu

 

[Zooqu1ko]

friendsssssssss!!!! I solved! everything works perfectly! yuhuuuuuuu

Please don't leave us in the dark and tell us how you fixed it.

 

[Taso]

You can't have this problem because you are not stupid! ahhaha
I'm a little ashamed. The problem was in a minidsp setting.
I was convinced that I had also tested an audiolab m-dac... but then I remembered that when I was about to test with audiolab... the coaxial digital out connector broke... and it distracted me... I ended the test due to a broken connector...and also because I was very angry.
I apologize if I stressed you out. I learned some things though! I have had minidisp for a few days, turned it on twice.

 

[voodooless]

I'm a little ashamed. The problem was in a minidsp setting.

Well isn’t that a familiar feeling…

I apologize if I stressed you out.

I’m sure you were a lot more stressed than we were. We’ve all been there at some point, and will be there again in the future. Glad it all worked out in the end!

 

[Taso]

 

[Taso]

I would like to ask another question.
Since I would like to properly adjust all the various gains of the audio chain, as well as the environmental correction, I was wondering: Is the digital output level of the Denon standard and therefore in perfect "tune" with the input of the miniDSP?
Furthermore, regarding the frequency... minidsp can work at 48khz or 96khz. From the measurements I did on the Denon... it seems to me that it comes out at 48khz.
Is this frequency fixed or adjustable?
I think it's better there are no different frequencies along the chain of digital connections, or am I wrong?
Thank you.

 

[Weeb Labs]

I would like to ask another question.
Since I would like to properly adjust all the various gains of the audio chain, as well as the environmental correction, I was wondering: Is the digital output level of the Denon standard and therefore in perfect "tune" with the input of the miniDSP?
Furthermore, regarding the frequency... minidsp can work at 48khz or 96khz. From the measurements I did on the Denon... it seems to me that it comes out at 48khz.
Is this frequency fixed or adjustable?
I think it's better there are no different frequencies along the chain of digital connections, or am I wrong?
Thank you.

The sample rate of the AVR is fixed at 48KHz and unless you are feeding the data to an ASRC, it will determine the sample rate of your signal chain. The I2S digital output levels are standard, with a 0dBFS reference.

 

[Taso]

La frequenza di campionamento dell'AVR è fissata a 48 KHz e, a meno che non si stiano inviando i dati a un ASRC, determinerà la frequenza di campionamento della catena del segnale. I livelli di uscita digitale I2S sono standard, con un riferimento 0dBFS.

Thank you. But so when I listen to a CD connected to the coaxial digital input of the Denon, it enters at 44.1khz 16bit and converted, by the Denon, into 48khz (how many bits?)... towards the coaxial digital output that I have implemented? thanks

 

[Weeb Labs]

Thank you. But so when I listen to a CD connected to the coaxial digital input of the Denon, it enters at 44.1khz 16bit and converted, by the Denon, into 48khz (how many bits?)... towards the coaxial digital output that I have implemented? thanks

Most Denon AVRs make use of SHARC DSPs with multiple onboard ASRC channels. Your 44.1KHz input will be resampled to 48KHz using 32-bit or 40-bit float, either at the DIR (handles SPDIF inputs) or the DSP.

 

[Taso]

Ok, thanks again for the answers and your time.
I enter the Denon with a CD player (via digital coax) and with an Apogee Rosetta 200 analogue-digital converter (recording studio device), which can output at various frequencies, up to 192Khz.
I think the best thing is to set it to 48khz to avoid resampling (by denon), is that correct?

I also have to thank you for your video. Thanks to you I now have digital output! Working!

 

[Weeb Labs]

Ok, thanks again for the answers and your time.
I enter the Denon with a CD player (via digital coax) and with an Apogee Rosetta 200 analogue-digital converter (recording studio device), which can output at various frequencies, up to 192Khz.
I think the best thing is to set it to 48khz to avoid resampling (by denon), is that correct?

I also have to thank you for your video. Thanks to you I now have digital output! Working!

You can certainly set your ADC to perform the resampling. It makes little difference whether the resampling is carried out by your ADC or by the DIR/DSP.

I'm glad that my video was helpful to you!

 

[voodooless]

Since I would like to properly adjust all the various gains of the audio chain, as well as the environmental correction, I was wondering: Is the digital output level of the Denon standard and therefore in perfect "tune" with the input of the miniDSP?

Most likely the gain differences of the AVR channels will be done via the analog volume control chips after the DACs. Maybe they also tweak the volumes control of the DAC a bit.. hard to say. You may find out with a bit of experimentation.

Furthermore, regarding the frequency... minidsp can work at 48khz or 96khz. From the measurements I did on the Denon... it seems to me that it comes out at 48khz.
Is this frequency fixed or adjustable?

It’s fixed. Note though that the MiniDSP will resample it again to its internal clock domain regardless of the input sample rate.

 

[Weeb Labs]

Most likely the gain differences of the AVR channels will be done via the analog volume control chips after the DACs. Maybe they also tweak the volumes control of the DAC a bit.. hard to say.

It is indeed a bit of both. The individual channel gain offsets are digital and then the analog volume control ICs are used to attenuate all channels at the output. Setting the system volume above ~82% will also raise the DSP output above 0dBFS, which is the source of the clipping often encountered during Amir's reviews.