Can someone please explain to me this signal path?

Not that it is too important but I want to know why 24/192 MQA signal went down to 24/96, just making sure I am setting things up the right way. As far as I know iDSD Nano is only a renderer and not a decoder.

My desktop DAC setup as follows:

MQA2
MQA3

Thank you.

Hello @Raymond_Ho,

The output of the MQA Core Decoder is 88.2 kHz or 96 kHz, regardless of the original MQA sample rate. In this 88.2 kHz or 96 kHz stream, the MQA signaling instructions cary the information for the MQA Renderer to complete the unfolding process to the original sample rate of the file, as shown in the “Authentication” stage.

-John

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Thank you, so am I correct that the max sampling rate of the Roon Core decoder is 96kHz?

Yes, not just for Roon, the max sample rate of any MQA decoder is 88.2/96 kHz.

AJ

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thank you, learn something new everyday.

What about a fully compatible MQA DAC\Decoder\Renderer, such as Mytek Brooklyn?

A fully MQA compatible DAC will decode to 88.1/96 and then render to the original encoded sampling rate (ORFS in MQA speak). Roon will detect such a DAC and set the Device Setting MQA Compatibility menu to “Decoder and Renderer”. On that setting Roon will ordinarily pass through the stream, complete with rendering information, and leave all decoding and rendering to the DAC. If you perform DSP in Roon (other than upsampling) then Roon will decode, perform the DSP and reattach the rendering information for the DAC. If you perform upsampling in Roon then it will decode in Roon and the DAC will not render.

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Thank you Andrew :slight_smile:

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Hi @andybob,

do you know what happen when you are passing an MQA signal to a DAC that is not MQA capable and you have up sampling enable?
I am passing MQA to a raspberry Pi with IQDac+ and I get Roon showing this path.

So authentication is happening and the first unfolding is done in roon up to 96kHz then volume levelling but the part I am not clear is the Sample rate conversion up to 192kHz. Is this is a legitimate up sampling?
thanks
Marco

Hi Marco,

I understand the upsampling to 192 kHz is occurring because you have set that output rate in Roon’s DSP engine. Roon is doing what you have asked it to do.

There is an important difference, however, between the first unfolding in the MQA decoder and the subsequent upsampling in the DSP engine. They do two different things.

The decoding process results in further musical content. It is substantially equivalent to having a 96 kHz hi-res file. This is a pretty good benefit for users with non-MQA DACs, like me. I say substantially equivalent because there are some differences, but I don’t believe they are audible.

In contrast, all upsampling is a “zero stuffing” process. The bandwidth of the signal is increased, but there is no further musical content added. The main purpose behind upsampling is to provide more room for filters to operate or to shift noise. Most modern DACs perform upsampling internally, but if they detect a high res incoming signal then they will bypass some or all of the internal upsampling.

The upsampling performed by Roon in the signal path above is not part of the MQA process. There is a further possible MQA process after decoding which is called rendering (this is the second unfold). Roon is not an MQA renderer. The rendering process appears to include upsampling with dynamic application of up to 16 filters. Roon can pass through the rendering information to a hardware MQA renderer, except where Roon is itself asked to upsample. Upsampling in Roon is incompatible with later MQA rendering.

Thanks Andrew,

I get that Roon up sampling is incompatible with later MQA rendering but does it compromise the quality?
If that is the case it would be nice if there was a way to automatically disable the up sampling if the DAC is not MQA compatible and Roon is playing MQA tracks, so that Roon does only the decoding.
In my case I have 3 set up one is using a Mytek Brooklyn that is MQA decor/renderer, the other is a Devialet that has not MQA capabilities and a raspberry pie that similarly to the Devialet has no MQA. In the case of the Devialet I am generally up sampling to DSD but, now that I have MQA albums in my library set up as primary album for the Brooklyn, when I play Radio Roon plays MQA tracks, it performs the first decoding and then up sample them to DSD before sending them to the Devialet. If this is process is compromising the signal and it would be better to simply send the MQA decoded without any other DSP process I would like to be able to have an automatic way tell Roon not to perform any DSP process if the track is an MQA.
Sorry for the convoluted explanation, I hope it makes sense
cheers
M

Hello @Marcor,

It is possible to get the behavior you are looking for, with a little bit of configuration! If you set the device to “Renderer Only” in the “Device Setup” screen, it will allow you to upsample to DSD for regular PCM tracks, and for MQA content will only enable the Core Decoder and ignore your upsampling options set in DSP Engine.

-John

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In my opinion, no. I upsample everything to DSD 512. Some people prefer PCM. The good news is that there are settings for everyone.

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Thanks John, yes it does make sense! Setting it up as Renderer only, applies the DSP like volume levelling but skip the upsamples as it expect that the DAC will do the Render so the signal is as intended. So for the purists that is the correct signal as intended.
But I tend to agree with Andrew, I just listened to MQA album upsampled to DSD64 and they sound great, so probably leaving the sample is a matter of taste a this point
Thanks all!

M

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