USB output
- Thread starter Klipscher
- Start date
Because SPDIF is one way with no feedback error correction. USB into ports designed for DACs like Schiit Unison have signal integrity advantages.
it will certainly be the case if a real new machine...
(the new formats corresponded to real needs in very strong evolutions in video.. but us in audio... seriously? ;-) *)
for the moment we don't even have a follow-up after this "little teaser a la wiim" on a revision of the "pro" with a new output stage..
*
(personal apartment:
it is the comparison between audio and video which is one of the main biases...
we are trying to boost the audio music market thanks to this...bisness is bisness.. and let's all admit with a smile that we are in a fairly consumerist position ;--) )
(the new formats corresponded to real needs in very strong evolutions in video.. but us in audio... seriously? ;-) *)
for the moment we don't even have a follow-up after this "little teaser a la wiim" on a revision of the "pro" with a new output stage..
*
(personal apartment:
it is the comparison between audio and video which is one of the main biases...
we are trying to boost the audio music market thanks to this...bisness is bisness.. and let's all admit with a smile that we are in a fairly consumerist position ;--) )
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There is no error correction in the isochronous usb audio transmission either.
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Isn't that a closed loop and packet resends possible?
What comparison? WiiM's products' outboard output is SPDIF only.
Even though I am in favor of a USB out in a future product, I think WiiM's SPDIF output is quite good and noise free.
Data cannot be resend because it's transferred isochronously - when the time frame is over it's over and the next one goes on. The DAC can decide to repeat an older sample or use an empty one, but cannot wait for the correct one.
I have a Wiim Pro in my main system which cannot use the USB-only input on the DAC card in my Schiit Lyr 3 preamp. The built-in DAC on the Wiim doesn't sound as good as the Schiit DAC. ( I also have a Raspberry Pi player that outputs via USB into that DAC, which is how I made the sound quality comparison.) So, I'm one of those who would like the Wiim to have USB output, as I don't want to add another box to my system just so I can use the coax/opitcal output of the Pro.
Klipscher
Active member
- Joined
- Nov 7, 2022
- Messages
- 133
Not sure if this also applies to streamers but might help explain why sound quality is suppose to be better with usb. I always heard that usb was the preferred input for dac’s. It’s the one that’s recommended for my dac.
So there is a lot of misunderstanding surrounding digital audio. With the 'bits are bits' argument often being used.
It's true in the sense that the actual CONTENT of the signal, the audio data itself, the 1's and 0's will either reach the DAC intact, or they will not.
There are no 'audiophile bits' and as far as data integrity goes, optical SPDIF, coaxial SPDIF, AES, USB, I2S or anything else will be able to get the exact same data to the DAC.
BUT, the issue with audio is that it is not purely about data integrity. TIMING is important too. If you have exactly the same audio content, (ie: Exactly the same PCM samples) but they are converted at different times, you'll get distortion.
This is called jitter.
USB is an 'asynchronous' protocol.
This means that the timing is actually controlled by the DAC.
A super simplified explanation is that audio data from your or PC is sent to your DAC, often in chunks at a time.
This is put into a buffer on the USB receiver of the DAC, and then the DAC uses its own internal clock (crystal oscillator) to determine when to convert these samples.
When the buffer is getting low the DAC instructs the PC to hand it some more data and it sends more to put into the buffer ready for conversion.
The DAC is dependent on its own clocks for timing accuracy, and whether you plug this DAC into a Mac, a PC, a Pi, or any other device, the jitter performance will be absolutely the same. The timing with which the source device sends data to the DAC makes absolutely no difference so long as the DAC always has the next sample in the buffer ready to convert.
SPDIF is a 'synchronous' protocol. And unlike USB, the source you use DOES have a direct impact on the quality of the output of the DAC, even if the data itself is completely identical.
Why? Because with SPDIF, the clock signal is actually sent by the source device (PC), NOT the DAC's own clocks.
Data is sent in a constant stream, accompanied by the clock signal, and so if there is additional jitter on that given clock signal, the DAC itself will be converting samples with less accurate timing and the analog output will be less accurate.
So there is a lot of misunderstanding surrounding digital audio. With the 'bits are bits' argument often being used.
It's true in the sense that the actual CONTENT of the signal, the audio data itself, the 1's and 0's will either reach the DAC intact, or they will not.
There are no 'audiophile bits' and as far as data integrity goes, optical SPDIF, coaxial SPDIF, AES, USB, I2S or anything else will be able to get the exact same data to the DAC.
BUT, the issue with audio is that it is not purely about data integrity. TIMING is important too. If you have exactly the same audio content, (ie: Exactly the same PCM samples) but they are converted at different times, you'll get distortion.
This is called jitter.
USB is an 'asynchronous' protocol.
This means that the timing is actually controlled by the DAC.
A super simplified explanation is that audio data from your or PC is sent to your DAC, often in chunks at a time.
This is put into a buffer on the USB receiver of the DAC, and then the DAC uses its own internal clock (crystal oscillator) to determine when to convert these samples.
When the buffer is getting low the DAC instructs the PC to hand it some more data and it sends more to put into the buffer ready for conversion.
The DAC is dependent on its own clocks for timing accuracy, and whether you plug this DAC into a Mac, a PC, a Pi, or any other device, the jitter performance will be absolutely the same. The timing with which the source device sends data to the DAC makes absolutely no difference so long as the DAC always has the next sample in the buffer ready to convert.
SPDIF is a 'synchronous' protocol. And unlike USB, the source you use DOES have a direct impact on the quality of the output of the DAC, even if the data itself is completely identical.
Why? Because with SPDIF, the clock signal is actually sent by the source device (PC), NOT the DAC's own clocks.
Data is sent in a constant stream, accompanied by the clock signal, and so if there is additional jitter on that given clock signal, the DAC itself will be converting samples with less accurate timing and the analog output will be less accurate.
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Matterhorn
Active member
- Joined
- Jul 5, 2023
- Messages
- 102
It is common. Many audiophile enthusiasts use the WiiM streaming device with an external DAC. There are some extremely good DACs like the new Cayin RU7 which only has a USB input. The request for a USB output is a heads up for WiiM. I'm convinced that competitors will be bringing affordable USB out streamers to market. WiiM can get started on the request now or play catch up later.
Just my two cents...
And make love, not (jitter) war
-The hand drawn figure you shown is exaggerated by many parsecs.
-Jitter can be at any stage of a domain conversion, not just in the transport interface.
-The clock precision and correction capabilities of modern DACs can minimize the side effects of jitter, making them quite urban legend-level. In jitter measurements, there are no systematic differences between interfaces and when present, they are related to the model, rather than the type of interface.
If someone wants a USB interface it should have other reasons, not the jitter itself.
The attached doc even old, explains jitter types and concludes that DAC's can manage it. Even better by nowadays DAC's.
I think jitter, can be the last of problems...
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