USB to toslink

[Andreitraian46]

Hello! I want a digital transport from the phone(iOS) to a toslink input of a DSP in car.
For the moment I’m using car modded AirPort Express that have toslink out and does 16/44. Some song have some harshness , it is present on midbass and midrange so it is the streamer the problem. My question is , what matters in USB to toslink? Jitter, clock, isolation? Implementation? Should i buy a separate linear source and a usb isolation? Would a cheap adapter like Smsl Po would work? Should i pull the trigger and buy an Rme adi-2 pro just as USB to toslink transport?

 

[DVDdoug]

Some song have some harshness , it is present on midbass and midrange so it is the streamer the problem. My question is , what matters in USB to toslink? Jitter, clock, isolation?

None of that is digital... If the digital data gets interrupted or corrupted you can get dropouts, clicks & pops, or just no sound at all. This isn't a perfect analogy but one flipped-bit in your bank account is just as likely to cause a one billion dollar error or a 1-cent error.

Usually the only time you get digital errors is when a stream of the Internet or network gets interrupted or if you get a read error from a "shiny disc".

...Lossy compression like MP3 or some Bluetooth can change the audio but usually it's VERY subtle unless you have a really low bitrate MP3 which can sound something like a 1st generation cell phone.

 

[Andreitraian46]

I think the harshness is due sampling , some are 16/48 that are downsampled in the airport to 16/44 then upsampled by the DSP dac , my guess. I stream from Apple Music , the stream is limited on WiFi to ALAC and 16/44.1.

 

[voodooless]

Some song have some harshness , it is present on midbass and midrange so it is the streamer the problem

That’s not a conclusion that followes.

16/44.1 should be plenty, especially in a car. The AirPort Express digital output should be decent enough as well by all accounts.

I think the harshness is due sampling , some are 16/48 that are downsampled in the airport to 16/44 then upsampled by the DSP dac , my guess. I stream from Apple Music , the stream is limited on WiFi to ALAC and 16/44.1.

Any resampling is generally inaudible. It causing harshness is not very likely.

I would look at the speakers, crossover and/or EQ setup.

 

[Vincent Kars]

This is rather dated (2005) but jitter performance is poor: https://www.stereophile.com/digitalprocessors/505apple
Maybe simply try a modern USB to S/PDIF converter.

PHIREE U2S 2019 & Douk Audio U2 Review and Measurements (Digital USB to S/PDIF Interfaces)

PHIREE U2S 2019 & Douk Audio U2 Review and Measurements (Digital USB to S/PDIF Interfaces) Update March 2022: Added comparison with the Douk Audio U2. Here is a quick review of the PHIREE U2S 2019 digital interface. This is basically some USB to S/PDIF converter that allows you to get USB...

www.audiosciencereview.com

 

[antcollinet]

This is rather dated (2005) but jitter performance is poor: https://www.stereophile.com/digitalprocessors/505apple
Maybe simply try a modern USB to S/PDIF converter.

PHIREE U2S 2019 & Douk Audio U2 Review and Measurements (Digital USB to S/PDIF Interfaces)

PHIREE U2S 2019 & Douk Audio U2 Review and Measurements (Digital USB to S/PDIF Interfaces) Update March 2022: Added comparison with the Douk Audio U2. Here is a quick review of the PHIREE U2S 2019 digital interface. This is basically some USB to S/PDIF converter that allows you to get USB...

www.audiosciencereview.com

Correct me if I'm wrong - but I can't see anything audible there at all.

 

[Vincent Kars]

In the IMD test there are spikes well into -60 dBFS

 

[voodooless]

In the IMD test there are spikes well into -60 dBFS

That’s for the analog output, though.

 

[antcollinet]

In the IMD test there are spikes well into -60 dBFS

Still not seeing it?

 

[wwenze]

Still not seeing it?

This probably

Tho I do question the audibility threshold of 19+20kHz IMD with both at a high output volume

 

[phofman]

IIUC that's analog output IMD - how does it relate to digital output jitter?

 

[Vincent Kars]

that's analog output IMD

All these measurements are the "same", feed the DAC with a digital signal and measure the analog out.
In the example above it is a IMD test by sending multi test tones to the DAC (F1 and F2), the spikes left and right of these test tones are conjectured up by the DAC.

 

[antcollinet]

This probably
View attachment 447168

Tho I do question the audibility threshold of 19+20kHz IMD with both at a high output volume

Where is that? Does't seem to come from the linked thread.

All these measurements are the "same", feed the DAC with a digital signal and measure the analog out.
In the example above it is a IMD test by sending multi test tones to the DAC (F1 and F2), the spikes left and right of these test tones are conjectured up by the DAC.

But IMD is not a result of jitter - it is the result of non linearities in the DAC so a problem with the DAC rather than the DDC. Again - unless I am misunderstanding, but I can't see where the chart is coming from.


Jitter - even if bad out of the DDC would normally be rejected by the clock recovery systems in the DAC.

 

[Andreitraian46]

I Eq the system a few times, phase looks all right at the crossovers, image is good , only some tracks are harsh , even if I play the driver like 300-350hz , that happen on midrange and midbass also , so it may be the source or just bad mixing of the tracks. Still I will try an Smsl or similar to see if it gets resolved.