Cambridge Audio CXNv2 upsampling everything to 384Khz

[Guy_Gampell1 (Guy Gampell)]

I have a new CXNv2, inbut it is not providing bit transparent output from Roon. Set up as follows:

Large lossless audio collection sitting on a network drive, indexed by Roon. The collection is mostly ripped CDs (about 1200), but I have about 110 Hi Res albums these are either hi res PCM or DSD.

Roon is running on a desktop PC, both the NAS drive and PC are on wired network connections to my router. The CXN is another room connected to my amplifier via optical digital (input 1) I also have a £30 Chromecast Audio connected to optical digital (input 2) via special 3.5mm cable/adaptor

With the external Chromecast I am getting bit transparency up to 24bit 96kz, but with the CXNv2 everything is upsampled to 384kbps even where it makes no sense

CXNv2 is running latest version, Service Pack: v018-a-075+a Firmware: 2.6+0.5+36
Roon is running v1.7 / build 528 on a Dell desktop tower with Windows 10.,
This Roon set up gives bit transparency up to 24b / 96 khz on my Chromecast Audio.

** here is what is happening with the CXN v2**

Regardless of input file format and sample rate, everything is being upconverted to 32bit 384KHz, here are some examples and more info referencing the images uploaded.

1., In the Roon menu for the CXN you can see I have every DSP feature disabled . Sample Rate Conversion is disabled and all filter functions are disabled

2. shows what I think is the root of the problem, despite the sample rate conversion being disabled, all these controls are live, I can fiddle around with the type of sample rate conversion filters, and the audio stream momentarily resets every time, but I really can’t see to disable sample rate conversion

In the Roon settings for CXN I also have it set to disable volume control (in the CXN) to have fixed output level

4. This shows the output result where the input file is at 96Khz sample rate, one sample rate conversion step, which is (mathematically) simple 4x Fs from 96khz to 384Khz. I was surprised to see any sample rate conversion (given the above) but a simple 4x filter is not tortuous on audio
   

   

5. Here the file is at 88.2Khz, and again it is being converted to 384Khz, since 88.2 is not an integer of 384, this is a far more complex filter and a filter I would choose to avoid. Perhaps I would have accepted to see 352.Khz sample rate at end point (again a 4x upscale) but certainly not 384k

I get a similar result for 16bit for 44.1Khz, again being upsampled to 384k, like 5 above, again a complex filter (upconversion to 352.8 would have been more sensible if really needed)

7. Finally and perhaps the most strange example. This shows what happened when I played a DSD file. The DSD bitstream is converted to 352.8, this is normal behaviour in most systems to render DSD. From there I would have hoped for bit transparency to the CXNv2 output, but no…. first it gets downsampled to 176.4KHz, then upsampled to 384Khz. Pretty tortuous.
   
   

Can you hear it? Absolutely, I spent many years working in recording studios, and am very able to detect the artefacts sample rate conversion leaves behind, my DSD files sound pretty horrible.

So conclusion to me is that the Sample Rate Conversion “disable” feature is broken , so for the moment by £30 Chromecast Audio remains my “go to” playback device.

The Chromecast Audio, plugged in to my amplifier sounds better than anything I have ever experienced out of my system. Bit transparency is worth pursuing and the CXNv2 is promoted as Roon ready and should be bit transparent for many more (and higher) sample rates than the Chromecast

Any ideas?

[BlackJack]

@Guy_Gampell1

So conclusion to me is that the Sample Rate Conversion “disable” feature is broken

This conclusion is false. As you can see, it’s the CXN (V2) that does the up-sampling (your points 4 and 5). This has nothing to do with Roon and it’s settings. If you use a digital output of the CXN (V2) then this up-sampling is irrelevant (not applied) as it only affects the D/A conversion (analog outputs).

About your point 7: What else do you expect here? The digital inputs of the CXN (V2) support a maximum sample-rate of 192 kHz.

PS: This is common behavior nowadays. Most (any?) of the integrated DAC chips do this (up-sampling to the highest supported sampling frequency before doing the D/A conversion) and offer filters (linear phase, slow roll-off, …) for the user to choose from. Buy a non-oversampling (NOS) DAC if you don’t want that to happen.

See also:

Cambridge 851N question

The up-sampling is a DAC feature. As you don’t use the DAC it seems not to be relevant for your use case. It looks like the digital input signal gets just passed trough to the digital outputs of the 851N. There is usually no conversion done (unless for compatibility reasons?) much as Roon handles it on default settings. I guess that the 851N does not signal the output in use (it most-likely doesn’t know that himself) as the outputs often work in parallel and the user is free to uses which ever o…

[Guy_Gampell1 (Guy Gampell)]

Thanks for your answer, but sadly I know this is incorrect information,

the sample rate conversion processing I am showing is unnecessary, the optical digital output of the CXN is what I am observing (and using) and it should be bit transparent to the sample rate of the source file. It isn’t . Yes it also determines the DAC on the CXN but I am not use the onboard CXNv2 DAC I am only coming out digitally to an external DAC which is locking to the sample rate coming out of the CXNv2. That sample rate should follow the file format sample rate with bit accuracy and no sample rate conversion, and it isn’t doing that., Roon can see that it isn’t and shows back where the unnecssary sample rate conversion is occurring. and as shown the “disable” selection of sample rate conversion isn’t working, even witn it set to “disable” I can adjust all the sample rate paraments, clearly it isn’t disabled!

[Guy_Gampell1 (Guy Gampell)]

I don;t expect the rendering device to upsample everything to its highest supported rate, unless sample rate conversion is enabled., with it disabled , the CXnv2 should follow the sample rate of the source file for bit transparency. The Chromecast Audio device does that exactly that
Chromecast Audio - play a 16bit 44.1 file - it deliver bit transparent digital output to my DAC at 16b 44.1
CNXv2 - play a 16 bit file - it delivers converted audio up scaled to 32bit 384Khz. to my external DAC

So a £30 dongle type device is giving me bit transparancey and does so for all its supported bit depths and sample rates up and and including 24b 96k, with no upscaling, and it sounds fab

the CXNv2 upscales even when sample rate conversion is disabled, so never delivers bit accurate digital output

It could be CXN issue, I have opened a ticket with Cambridge Audio, so seeking to understand where the issue lies,

[AndyR (Andy)]

Looks to me that the CXN is doing the upsampling…

If you are not using the CXN DAC, and wish to use optical in to the rest of the chain, I think the CCA is probably the better choice.

[BlackJack]

@Guy_Gampell1

and as shown the “disable” selection of sample rate conversion isn’t working

The only thing you have shown with your screenshots is that Roon doesn’t do any sample-rate conversion (see your examples 4 and 5). If the digital outputs of the CXN (V2) don’t follow the input sample-rate or you’re otherwise unhappy with what the CXN (V2) does with the incoming signals please let Cambridge Audion know about it.

Update: I see you did that already.

[Guy_Gampell1 (Guy Gampell)]

You are correct as to where the sample rate conversion is happening I believe (in the CXN) but what I am not sure is where is the control point for those capabilities. The reason the problem may be with Roon, is that the feature to disable the CXN sample rate conversion control settings for CXN in the Roon app (just as the is the feature to disable volume control) . So I am wondering if Roon had an API given to them by Cambridge Audio such that the Roon app becomes the “janitor” running around controlling those elements of the CXN. I’d like to hear from a Roon developer if that is the case.

[BlackJack]

@Guy_Gampell1

CNXv2 - play a 16 bit file - it delivers converted audio up scaled to 32bit 384Khz. to my external DAC

Why do you believe that?

@From the CXN (V2) Manual; Page 6

5. DIGITAL OUTPUTS

The CXN v2 digital outputs enable a separate DAC (digital to analogue
converter) or digital recording device to be connected. Refer to the
‘Operating instructions’ section for more information.

Two concurrent digital outputs are available. Note that these outputs pass
through the currently selected audio source unprocessed, i.e. no volume
control or up-sampling is performed on the digital outputs.

Coaxial – To obtain best results, use a high quality 75 ohm digital RCA
interconnect cable.

TOSLINK Optical – Use a high quality TOSLINK fibre optic interconnect
cable designed specifically for audio use.

[Guy_Gampell1 (Guy Gampell)]

CCA is great but only bit transparent up to 96Khz and I have some files which are 192, or 176.4, and no DSD support. But you are right, if I can;'t get the CXNv2 to give me a bit transparent digital output with no sample rate conversion, then I will be using the CAA not the CXNv2 to enjoy 99% of my music.

[Guy_Gampell1 (Guy Gampell)]

Thanks, it depends where the upsampling is done, but I am not getting “purple” indicators on the Roon app which I do get using the Chromecast, I am getting “white” indicators, And even if I was using the DAC output of the CXN I would still want to avoid sample rate conversion, and have the DAC rate follow the file format rate.

[Guy_Gampell1 (Guy Gampell)]

So, I agree the sampe rate conversion is being done by the CXN (which is why I reached out to Cambridge Audio), but since the control to turn on/off sample rate conversion is within Roon software I also reached out here.
This is an interesting comparsion. a file at 24bi 88.2Khz sample rate played back on Chromecast Audio, no sample rate conversion, bit transparent.
Same file played back to CXN, upscaled to 96Khz, which is undesirable. It does indeed look like an issue in the CXN, unless the “bug” is that the feature to disable CXN sample rate conversion as presented in the CXN control panel of the Roon app, is not working.

[BlackJack]

There is no mention of a 96 kHz sampling frequency anywhere in your example pictures. Roon is sending a 88.2 kHz stream to the CXN (V2). As the CXN (V2) does up-sampling from 88.2 kHz to 384 kHz for the D/A conversion, I assume that the CXN (V2) indeed receives a 88.2 kHz stream.

[AndyR (Andy)]

I think your screenshot is showing Roon’s sample rate conversion capabilities; I don’t think Roon is exposing functionality (ie control of the upsampling) within the CXN that is not available on the device itself.

The manual also suggests that the TOSLINK output of the CXN is limited to 96KHz; this is consistent with the usual advice that 192KHz might work, but is neither guaranteed nor recommended.

[jobseeker (Paul)]

I thought automatic upsampling to the max capacity of the DAC was inherent in the Cambridge Audio philosophy in recent years. Perhaps I’m wrong.

[Mike_O_Neill]

It is and has always been even in the DAC magic 100

Out of interest why are not using the CXN DAC via the analogue RCA outputs to your amp it surely be a better DAC than a CCA, why have the CXN in the first place , you could go Roon to CCA 96 then to your amp.

I am confused

The CXN has always upsampled internally then drops the output according to the type, optical 96, coax 192. Mine is the V1 and does that , download the Reference Manual from CA it explains it.

I am currently listening my CXN at 192 from a 192 source via a coax link to my headphone amp DAC , it shows 192

As @BlackJack points out that’s how the CXN does it processes at 384

[Mike_O_Neill]

Just a bit of background now I got to my computer, watch this, Ben explains all …

This is taken from the CXN Technical Specification

I even found reviews for the DAC Magic 100 (I had one of these too) , which was the original Stream Magic implementation along with the DAC Magic Plus 100, both extolling the virtues of ATF2

As far as I know the practice of internally upsampling to the max the DAC chip can handle is quite a common practice , My Audiolab M-DAC does the same.

What you are seeing is (I believe) by design and indeed nothing to do with Roon

Hope this helps ,

My advice would be use the CXN to the hilt , use an analogue pair out to your amp. The DAC is superb and a true hi fi component and has won loads of What Hi Fi awards

You’re lucky you have the v2 mine’s the V1

[Henry_McLeod (Henry)]

The control to turn sample rate on and off refers to Roon software only. There are two characteristics of Cambridge Audio digital gear that is pretty commonly known. It internally upsamples everything to 384k (and was one of the first companies to do that) and it doesn’t do DSD. There isn’t really anything controversial in the original post. I have a streaming DAC that I can select how it treats its input and it does show that in the signal path. But that isn’t controlled via Roon, it is via the remote for the device and Roon is versatile enough to show that in the signal path.

[Guy_Gampell1 (Guy Gampell)]

Hi My Amp is a Cambridge Audio Edge A, the DAC is better than in the CXNv2, but it’s not a bad idea, i did try the balanced analogue output from the CXN, but preferred the DAC in the Edge A

Edge A

[Guy_Gampell1 (Guy Gampell)]

OK, if this is the case I will be disappointed, I messaged Cambridge Audio before buying the V2 (I had a v1) and discussed specifically the topic of bit transparency.

[Guy_Gampell1 (Guy Gampell)]

@Mike_O_Neill

As far as I know the practice of internally upsampling to the max the DAC chip can handle is quite a common practice , My Audiolab M-DAC does the same.

What you are seeing is (I believe) by design and indeed nothing to do with Roon

Thanks all for your help, it makes sens as a technical explanation as to what is going up, the CXNv2 is upsampling to it;s highest supported feature, but from and audio engineering point of view that makes no sense for critical listening. I really want a networkable Streamer that will give me bit transparency to a digital output (networked to Roon so Roon Ready), the DAC will just follow and lock to the incoming sample rate, which in turn should be clocked from the sample rate of the file source without sample rate conversion.

I’ve done plenty of listening tests over the years (including several years working in high end recording studio), to know the artefacts sample rate conversion leaves behind. If I am doing critical listening indeed my job involves critical listening to source files which may or may not have artefacts in them, I want to know any artefacts I hear are in the source, not in the replay signal path.

I will continue to take this up with Cambridge Audio, who should not have told me the CXNv2 was roon ready in response to a question about bit transparency replay with Roon