USB output need to be cleaned?

[somy]

Pro-ject has an interesting product Stream Box S2 Ultra which is essentially rpi with Volumio with “audio optimised” usb output:
https://www.project-audio.com/en/product/stream-box-s2-ultra/
Interesting they claim the usb output can also help to clean the USB noise PC (so basically you can connect your pc to DAC via the device).
What I don’t understand is why there is a need to clean USB output (audio optimised to put it another way)? As I understand it’s purely digital with checksum etc, and an async DAC controls the clock so noise should not affect SQ at all. Or do I miss the point?

 

[DSJR]

Don't most dacs these days offer USB noise immunity? Amir's tests seem to indicate this fact I think...

 

[AnalogSteph]

This unit appears to be a small computer. Whether the "USB detox" functionality means that it's got galvanic isolation for the DAC USB and power supply, I can't tell, nor where Ethernet shield is connected.

 

[Theriverlethe]

Ridiculous...

Don't most dacs these days offer USB noise immunity? Amir's tests seem to indicate this fact I think...

Immunity is a bit of a stretch, but I wouldn't expect a small low-power device like this to have noise problems in the first place.

 

[Beershaun]

Prior to the rpi4 the usb shared the same bus as the ethernet port. So it limited the bandwidth available and created pops and clicks and audible noise. So fixing that is nice.

 

[Chromatischism]

Pro-ject has an interesting product Stream Box S2 Ultra which is essentially rpi with Volumio with “audio optimised” usb output:
https://www.project-audio.com/en/product/stream-box-s2-ultra/
Interesting they claim the usb output can also help to clean the USB noise PC (so basically you can connect your pc to DAC via the device).
What I don’t understand is why there is a need to clean USB output (audio optimised to put it another way)? As I understand it’s purely digital with checksum etc, and an async DAC controls the clock so noise should not affect SQ at all. Or do I miss the point?

USB uses a conductive (metal) connection to the PC. All of the noise from the PC can and does travel through that wire.

I had a lot of trouble with this while using powered speakers on my desktop. My PC uses an ASUS Z170 motherboard with Realtek onboard audio. It wasn't until I switched to the optical out that the noise coming from the speakers was eliminated.

This poses a problem for me as I want to switch to using a laptop to control my audio system. Most of these laptop PCs do not have optical interfaces. Mine would need to use HDMI, so I'll need to find a way to ensure I get a clean signal. I haven't tested it yet. It may be that it's fine and doesn't suffer the same issues...we'll see.

 

[BillG]

My PC uses an ASUS Z170 motherboard with Realtek onboard audio. It wasn't until I switched to the optical out that the noise coming from the speakers was eliminated.

There was something wrong with the implementation in that case then. I've used USB Audio on machines that were significantly older and I've never had to do anything special to them.

 

[Chromatischism]

There was something wrong with the implementation in that case then. I've used USB Audio on machines that were significantly older and I've never had to do anything special to them.

I know I'm not alone on that, but it also varied with the speaker. I had Yamaha HS7's, Emotiva Airmotiv's, and Mackie MR624's. Some seemed to have the ability to reject the noise better than others. Unfortunately the ones that sounded the best did not have that ability, so optical it was.

 

[solderdude]

I had a lot of trouble with this while using powered speakers on my desktop. My PC uses an ASUS Z170 motherboard with Realtek onboard audio. It wasn't until I switched to the optical out that the noise coming from the speakers was eliminated.

This is a very clear case of a groundloop. It has nothing to do with 'clean' power or 'improved signal quality'.
All you need in this case is an USB isolator. This basically is what the optical path does. It breaks the groundloop.

 

[PeteL]

Don't most dacs these days offer USB noise immunity? Amir's tests seem to indicate this fact I think...

Basically, If you look at the USB signal trough a oscilloscope and it's so noisy that visually you can't tell if it's a low level or a high level on some segments, no DAC will be able to reliably tell neither. It happens, I've seen it.

 

[PeteL]

Pro-ject has an interesting product Stream Box S2 Ultra which is essentially rpi with Volumio with “audio optimised” usb output:
https://www.project-audio.com/en/product/stream-box-s2-ultra/
Interesting they claim the usb output can also help to clean the USB noise PC (so basically you can connect your pc to DAC via the device).
What I don’t understand is why there is a need to clean USB output (audio optimised to put it another way)? As I understand it’s purely digital with checksum etc, and an async DAC controls the clock so noise should not affect SQ at all. Or do I miss the point?

I won't comment on the value of such a device, but it's a mistake to think of a signal travelling trough a wire as "purely digital" It's a variable pulse width waveform, subject to perturbations. The USB audio Class 2 protocol does a parity check, but can't do correction. It's rarely a problem, the key word is rarely.

 

[solderdude]

In that case any 'cleaner' will not be able to fix the signal either.

In this case it is very clear the the culprit is common mode currents, not data or USB 5V.

 

[MadMan]

USB uses a conductive (metal) connection to the PC. All of the noise from the PC can and does travel through that wire.

I had a lot of trouble with this while using powered speakers on my desktop. My PC uses an ASUS Z170 motherboard with Realtek onboard audio. It wasn't until I switched to the optical out that the noise coming from the speakers was eliminated.

This poses a problem for me as I want to switch to using a laptop to control my audio system. Most of these laptop PCs do not have optical interfaces. Mine would need to use HDMI, so I'll need to find a way to ensure I get a clean signal. I haven't tested it yet. It may be that it's fine and doesn't suffer the same issues...we'll see.

Are you saying you were using the onboard audio lineout, then switched to optical ?

 

[Chromatischism]

This is a very clear case of a groundloop. It has nothing to do with 'clean' power or 'improved signal quality'.
All you need in this case is an USB isolator. This basically is what the optical path does. It breaks the groundloop.

Ground loops are 60 Hz. This was more like pink/white noise but not as consistent.

 

[Chromatischism]

Are you saying you were using the onboard audio lineout, then switched to optical ?

Yep.

 

[PeteL]

This is a very clear case of a groundloop. It has nothing to do with 'clean' power or 'improved signal quality'.
All you need in this case is an USB isolator. This basically is what the optical path does. It breaks the groundloop.

Could be, but generally a ground loop would create a hum at the main frequency, not noise. A large error rate on the other end is noise, if those errors are of a random nature.

 

[PeteL]

Are you saying you were using the onboard audio lineout, then switched to optical ?
Yep.

So why would it have something to do with USB? If you are using line out.

 

[Chromatischism]

So why would it have something to do with USB? If you are using line out.

Sorry. I tried both, with the same result.

 

[solderdude]

Everything points to a groundloop. (it is more often weird noises than 'clean hum')

Options are:
Properly ground the PC/laptop
use optical
use an USB isolator (galvanic isolation)
Use balanced cables to the active speakers (when the DAC and speakers have these connections)

 

[somy]

I won't comment on the value of such a device, but it's a mistake to think of a signal travelling trough a wire as "purely digital" It's a variable pulse width waveform, subject to perturbations. The USB audio Class 2 protocol does a parity check, but can't do correction. It's rarely a problem, the key word is rarely.

Well I assume there is a mechanism to resend the incorrect packet in USB protocol so in theory "correction" will be done automatically at protocol level, right? Otherwise we can't trust the data we copy into a USB harddrive. The question is, does the "error" have any impact on SQ? As I read most DAC has async USB so there shouldn't be any jitter if a cache is used.