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Spdif to usb!?


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18 hours ago, Ittaku said:

There are boards that can do this if you're into DIY, but I'm not aware of a standalone device you can buy off the shelf that will.

Which boards?

Does the USB output operate only in isochronous mode or is there some kind of ASRC going?

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18 minutes ago, kdoot said:

Which boards?

Does the USB output operate only in isochronous mode or is there some kind of ASRC going?

Stuff like this:

https://www.diyinhk.com/shop/audio-kits/142-xmos-multichannel-high-quality-usb-tofrom-i2sdsd-spdif-pcb.html

You now know as much as I do. I bought one but an ailment which is causing deafness made me lose interest in pursuing getting it working.

Edited by Ittaku
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An RME PCIE audio card can accept coax spdif or AES3 as an input and using the RNE mixer outputs to the computer’s sound card or ASIO compatible USB DAC.

 

Kind of an odd process , but technically possible. A DAC can accept coax direct so not sure why the added complexity would be worthwhile plus add noise and less than optimal RME mixer.

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Let me just explain the issue a little bit. 

 

USB supports two-way communication but is a master/slave arrangement where everything is coordinated by the "host". A USB-only DAC is not a host, it is a "device" which needs a host to send it audio data. So your hypothetical converter needs to have at least the smarts of something like a Raspberry Pi or other small computer in it to play the role of USB host.

 

SPDIF is a one-way communication. A SPDIF receiver watches the voltage switching between two levels and its first job is to try and "tune in" to the transmission frequency. Just about everybody supports 44.1kHz (I recall a Bel Canto CD player that would only output at 96kHz, after doing some sample rate conversion) but no two clocks run at exactly the same rate so the receiver has to adjust itself, usually with a PLL, to track the overall average rate of the incoming data. Major point: SPDIF runs at its own rate.

 

We learned early on in computer-based hifi that there are two modes of operation for USB Audio and one of them sounds *bad*. It comes down to clocking: if the audio device (the DAC) is in control of the flow of data, using its own local clock and a USB mode called "asynchronous", then you could get good results. If the host is in control of the flow with a USB mode called "isochronous", you could not. 

 

So the problem with this converter idea is that you can't simultaneously have the DAC in control of the flow of data via USB asynchronous mode while the USB host is receiving that data from a SPDIF source that runs at its own rate. The USB system would have to operate in isochronous mode, which is how you get the worst kind of digital sound.

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I still wonder why would anyone want to do that? USB DACs generally expect data stream from a computer - so, yes in theory you could input a SPDIF signal into an audio interface card, transfer it into a computer and output that through a USB out of that same computer into a DAC. Again, why would you do that? 

 

Something like this: 

https://www.sweetwater.com/store/detail/Studio1824C--presonus-studio-1824c-usb-c-audio-interface

Edited by Decky
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I'm not sure why you aren't getting a straight answer to your question. Just Google "SPDIF to USB converter" or something similar. SQ? In some cases it may even improve the SQ. 

Prices range from about $40 US to $2000 US. There are some that also do AES. 

Even my little iFi nano iOne DAC does USB to SPDIF conversion. 

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1 hour ago, firedog said:

I'm not sure why you aren't getting a straight answer to your question. Just Google "SPDIF to USB converter" or something similar. SQ? In some cases it may even improve the SQ. 

Prices range from about $40 US to $2000 US. There are some that also do AES. 

Even my little iFi nano iOne DAC does USB to SPDIF conversion. 

One of my all-time favourite digital audio devices is the Audiophilleo. It's a USB to SPDIF converter. I understand its theory and operation very intimately, and it's extremely similar in principle to many other devices on the market which as you say range from very cheap to quite an investment. The thing is, they're the exact opposite of what the original poster is asking for: they let you get audio out of a computer using USB and feed it to a DAC that only has a SPDIF input. 


The reverse process technically can be done, but it's full of serious challenges and compromises some of which I outlined in my previous comment.

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2 hours ago, Decky said:

I still wonder why would anyone want to do that? USB DACs generally expect data stream from a computer - so, yes in theory you could input a SPDIF signal into an audio interface card, transfer it into a computer and output that through a USB out of that same computer into a DAC. Again, why would you do that? 

 

Something like this: 

https://www.sweetwater.com/store/detail/Studio1824C--presonus-studio-1824c-usb-c-audio-interface

USB DACs *always* require a data stream from a computer of some sort. It can be a very small computer, but regardless that's what's required. 

 

The device you linked to would probably be able to do the job, but the chain would be:

SPDIF source (determines the overall clock rate)

PreSonus (SPDIF in, USB out)

Computer (USB in, USB out using isochronous mode)

DAC (USB in)

 

It's expensive and complicated, and because of the isochronous USB it'd probably sound pretty ordinary.

 

I tried to find another device on the market that could replace that PreSonus box at a lower price... and couldn't!

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I have a USB only DAC which I like a lot, but use digital room correction with Dirac so all my sources go through a Minidsp which outputs in coax.

I still wonder why would anyone want to do that? USB DACs generally expect data stream from a computer - so, yes in theory you could input a SPDIF signal into an audio interface card, transfer it into a computer and output that through a USB out of that same computer into a DAC. Again, why would you do that? 
 
Something like this: 
https://www.sweetwater.com/store/detail/Studio1824C--presonus-studio-1824c-usb-c-audio-interface
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5 hours ago, o2so said:

I have a USB only DAC which I like a lot, but use digital room correction with Dirac so all my sources go through a Minidsp which outputs in coax.

I think you are over-complicating things a bit there. You are effectively using (or want to use) two digital "conditioners" or x-overs, not sure if that is the best way without knowing more about your system.

 

Where are you sending that miniDSP SPDIF signal now - it has to be a DAC of some sort? I also do not understand where is the Dirac room correction - it the DAC that receives the SPDIF or in the USB DAC?  Can you describe the system with models of equipment and connections between them, so I can understand what is going on there. 

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On 14/09/2019 at 3:49 AM, Decky said:

I think you are over-complicating things a bit there. You are effectively using (or want to use) two digital "conditioners" or x-overs, not sure if that is the best way without knowing more about your system.

 

Where are you sending that miniDSP SPDIF signal now - it has to be a DAC of some sort? I also do not understand where is the Dirac room correction - it the DAC that receives the SPDIF or in the USB DAC?  Can you describe the system with models of equipment and connections between them, so I can understand what is going on there. 

Thanks mate.

 

my sources are:

1. Roon via a streamer that outputs in toslink

2. Record player which is converted to digital coax by the phono stage

 

1 and 2 enter a Minidsp box, which is all digital and performs the Dirac room correction, then outputs the signal in digital coax.  This then enters a DAC.

 

I would like to replace my current DAC with a different  one that I prefer but has USB input only. Hence my question.

Edited by o2so
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I am afraid you limited yourself to the main SPDIF stream - you have to find a DAC that you like. USB input is just another digital conversion of the data stream, there is nothing special about it. Eventually all those 1s and 0s get to the main DAC chip and get spit out as voltage that is then amplified. That amplification or the output stage is really 90% of the DAC sound signature. Modern DAC chips, if installed and implemented properly should remain indistinguishable to human hearing. Try to find a DAC with a SPDIF input that has a decent output stage and you should be right. Sell the rest that you do not like and problem solved. 

 

Now, as far as I am concerned (and my not so humble opinion), I would not use toslink out of the streamer or use ADCs to digitise the phono signal (sacrilege!) or for that matter, use room correction - but that is only me. Your system, your circus and you monkeys. Have fun.   

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13 minutes ago, Decky said:

I am afraid you limited yourself to the main SPDIF stream - you have to find a DAC that you like. USB input is just another digital conversion of the data stream, there is nothing special about it. Eventually all those 1s and 0s get to the main DAC chip and get spit out as voltage that is then amplified. That amplification or the output stage is really 90% of the DAC sound signature. Modern DAC chips, if installed and implemented properly should remain indistinguishable to human hearing. Try to find a DAC with a SPDIF input that has a decent output stage and you should be right. Sell the rest that you do not like and problem solved. 

 

Now, as far as I am concerned (and my not so humble opinion), I would not use toslink out of the streamer or use ADCs to digitise the phono signal (sacrilege!) or for that matter, use room correction - but that is only me. Your system, your circus and you monkeys. Have fun.   

Thanks for the advice.

I do not have a dedicated room for music so physical room treatment is not an option, especially to manage bass response. Hence digital room correction is the corner stone of my system, in fact it generates the most obvious audio improvement than any other component I have ever owned. Especially when entirely done in the digital domain like I am doing.

 

Digitising the phono signal is not a sacrilege to me, in fact when done properly (I am using a PS Audio phono converter -which does hi res conversion live), it is absolutely indistinguishable from the analog out. 

 

 

Edited by o2so
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RME ADI 2 Pro fs would probably do it, as well as being a DAC, as well as taking analogue input, as well as giving you bass management via 2 separate 5 band para eq, as well as having 2 DAC chips meaning digital crossover abilities and feeding mains/sub via separate outputs. I think the analogue input also has its own 5 band para eq too.

I know it’s not really what you’re asking, however it would seem to be a good fit for your setup?!

No remote though, if that’s important...

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I don't have any doubts that it can be done but the price that has to paid with sound quality is not going to be small. There is heaps of pro equipment suitable for the job but triple (or more) digital conversion, with different clocks and sometimes questionable quality of components cannot result in something that I would call "audiophile quality" (with full understanding that is highly subjective label). Also, convenience is sometimes more important but hi-fi was never about convenience anyway. 

 

Regarding the phono to SPDIF - again, it can be done better and worst with terrible results and not so bad results but either way - any ADC conversion removes the essence of the phono signal - the bandwidth - and introduces a range of digital processing artifacts that one has to deal with somehow. The gain can be on the digital processing side and overall DSP conditioning -which is exactly what is the case here - so, again, I understand the choice but, not exactly how I would approach the problem.  

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Thanks mate. Are you able to point me to any objective tests or measurements indicating that any ADC reduces the bandwidth of an analogue phono signal and introduces the artifacts you mentioned? I'd be interested to read because as I said there is no audible difference to me even when listening through highly revealing gear ( Focal Utopias).


I don't have any doubts that it can be done but the price that has to paid with sound quality is not going to be small. There is heaps of pro equipment suitable for the job but triple (or more) digital conversion, with different clocks and sometimes questionable quality of components cannot result in something that I would call "audiophile quality" (with full understanding that is highly subjective label). Also, convenience is sometimes more important but hi-fi was never about convenience anyway. 
 
Regarding the phono to SPDIF - again, it can be done better and worst with terrible results and not so bad results but either way - any ADC conversion removes the essence of the phono signal - the bandwidth - and introduces a range of digital processing artifacts that one has to deal with somehow. The gain can be on the digital processing side and overall DSP conditioning -which is exactly what is the case here - so, again, I understand the choice but, not exactly how I would approach the problem.  


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No need for objective measurements to prove the point - any analogue source has an infinite bandwidth and if you digitise it you are limiting that bandwidth to that of the ADC used in the process. In addition to that, you are on the mercy of the ADC implementation and clocking and subsequent signal processing to preserve as much of the sampled data in its original form. If done in 24bit words with 192KHz sampling rate you will get almost all of the meaningful data from your vinyl captured and you should have enough headroom left in those 24bits to deal with various smart ways of S/N ratio maximisation. If, however you sample it with 16bit 44.1KHz - you are just creating (very badly) a red-book CD with a shitload of noise and effectively a situation where you are better off just using a CD. This is on top of the fact that ADCs for audio are still not fully optimised and most of the manufacturers are using generic industrial ADCs. I am not saying that sampling an audio signal is harder than say, measuring vibrations of a rocket engine, but it does have some peculiarities. The revolution of optimising audio specific DACs never really happened with ADCs. There is a lot of stuff aimed at high-end pro-audio market and pro-recording devices and maybe those are good enough or even better. I just checked some new Ti audio specific ADCs - they are really good but how much they are used in home audio I really do not know. For an average consumer it is also very hard to get that data from the manufacturer.   

 

All of that is just technology beyond any subjective test of audibility.  The question is - can you hear that? Well, I don't know that since that diverges from objectivity. For me audio technology should be more focused on "how things should be done" rather than "what can I escape with" scenarios.  

Edited by Decky
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O2so what is the DAC you would like to be using?

Your NuWave Phono Converter is a gem of a thing.

Doing room correction in digital domain prior to DAC is a great approach.

Finding the right DAC is your main challenge now, but USB input is not going to work out well with the other gear you currently have.

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