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Sonos: Hi-Res ready or not, Qobuz finds the truth

By Harry Chancellor |

What products do Sonos offer by way of High Resolution? That's the question we asked ourselves whilst nosing around the innards of the Sonos Connect, as we like to do, so we delved further into the subject.

The question of what Sonos has in its devices to deal with High-Definition audio files has been racking the brains of audiophiles and has incited heated debate on online forums (97 pages on Sonos' message board alone).

Here is Sonos' most recent statement referring to support for Hi-Res audio on its devices:

The original request is to support 24 bit audio tracks on Sonos components, to which the status is still Not Planned. We are constantly monitoring these threads and will continue to pass on your feedback to our product teams.

This response seems a little vague to us, and at the very least says the brand is at least looking into the problem (albeit whilst putting it to the back of the shelf).

Sonos could not be more clear on their site, as they indicate the frequencies that are compatible with their devices as well as the accepted bitrate, all the while affirming that there is never any "downsampling". The maximum bitrates are those of CD quality, or 1411kbps, which tests confirm: audio files above 16-bit/44.1kHz are not compatible.

Whether or not you are streaming over SonosNet or Ethernet wired Sonos components, Sonos does not downsample audio streams in any way.

The above information should put an end to the debate, but we would still like to settle some confusion caused by Sonos' announcement "Ready for the Hi-Res experience".

This is a little sneaky as they're referring to CD-quality, but fo those who are used to MP3, CD-quality could be seen as High Resolution.

Deezer has recently launched their high definition streaming via Sonos across the world. A recent Belgian article said: "Deezer Elite proposes a service where Deezer customers can listen in FLAC format (Free Lossless Audio Codec) with no losses at 1411 kbps minimum. This constitutes a real leap in sound quality from the 320 kbps of MP3."

No comment.

At Qobuz, we have decided the best thing to do is take a closer look at the components of a Sonos Connect to try to see whether this device could eventually be HD-compatible; that is to say that is can accurately reproduce files between 24-bit/44.1kHz and 24-bit/192kHz.

The circuit used for digital-to-analogue conversion i a Cirrus Logic CS4265, which is compatible with signals up to 24-bit/192kHz. The aforementioned oscillator is a 11.289MHz model.

To better understand the network components, we enlisted the help of one of Qobuz's computer engineers to enlighten us (thanks Pierre!).

At the centre of Sonos Connect network card is a Hitachi SH7751R processor, next to which we can see a 512KB Atmel AT27LV512 ROM, which most likely includes the code to initialise this part of Connect. This non-volatile memory OTP (One Time Programmable) and cannot be erased or rewritten once it has been programmed.

Under this ROM is an ST Microelectronics NAND256W3 Flash memory, offering a capacity of 256 MB.

This is an EEProm (Electrically-erasable programmable read-only memory), which means that it can be erased electronically and then be rewritten. This type of memory allows for updates and safeguards configurations and settings.

The two other circuits found on this card are an Ethernet Realtek RT8139CL controller and an Ethernet Marvell 88E6060 switch, allowing to switch between the signals originating from the wired RJ45 input and those coming from the WiFi card, which here is an Alpha Network WMP-N06.

On the other side of the network card, along with the WiFi module, is a Texas Instruments TMS320VC5402 DSP (digital signal processor) with a protective shield and two RAM by Sony (K4S281632B models). There is also a Renasas RSF2110 micro controller which handles the overall management of electronics.

Our conclusions

Above all, it's hard to understand why, if they have the capability, Sonos do not proceed with an update allowing its devices to read high-resolution audio from the network.

So what has our investigation taught us?

We initially thought that it was the STMicroelectronics Flash memory that was stopping Sonos from updating the firmware to allow for Hi-Res audio, but the analysis of the components used by Sonos by an engineer of network readers who we contacted brought up other hypotheses.

The processor used for the network - a SH7751R - does not visibly have a I2S bus (necessary for thee function of the digital-to-analogue conversion chip), so Sonos would be obliged to create one with the Texas Instruments TMS320VC5402 DSP.

The TMS320VC5402 is an old model, released in 1998, so only works at 16-bit.

It would hence be complicated to treat 24-bit audio signals with this DSP, which works with the SH7751R processor via a connection which does not have a sufficient bitrate to transmit Hi-Res audio files.

Elsewhere, we noticed a 11.289 MHz oscillator in the digital-to-analogue conversion network whose output is connected to pin 29 of the CS4265 (MCLK or Master Clock) through a 100Ω resistor (labeled 101).

Even in high-resolution audio playback with the Connect, the master clock's frequency of 11.289MHz would limit the decoding capabilities of the CS4265 DAC for files sampled at 44.1kHz, 88.2kHz and 176.4kHz.

As the Sonos Connect is, files of 48kHz, 96kHz and 192kHz cannot be treated by the CS4265 DAC because synchronisation would be impossible - 11.289MHz being a multiple of 44.1kHz (x 256) and not of 48kHz. This seems to be in contradiction with Sonos' statement.

On the product guide: Native support for 44.1kHz sample rates. Additional support for sampling rates of 48kHz, 32kHz, 24kHz, 22kHz, 16kHz, 11kHz and 8kHz.

"Additional support"? For 48kHz, that would be an MP3 on iOS, so an upgraded treatment application.

Elsewhere we noticed that the DSP's quartz is at 20MHz, so cannot offer divisions of 44.1kHz or 48kHz, and so could not geerate a master clock adapted to files of 44.1kHz or 48kHz (or multiples thereof). For comparison, the processors used in the USB interface all include two quartz's: one at 22.579MHz (512 x 44.1kHz) and the other at 24.576MHz (512 x 48kHz).

Are the limitations on reading Hi-Res files restricted to the DAC or are other hypotheses also to blame? We think the latter, and that probably explains the upholding of the status quo at Sonos.

Original article by PHILIPPE DAUSSIN
Translation by RACHEL HARPOLE