Yes. I also have the Audiophilleo USB to S/PDIF bridge that I will test with. I will also take apart the AQ and do a write up/show images of what is inside it. Time allowing, I will also scope out electrically and see what is there. Or isn't.
How much are the other devices like it by the way?
Absolutely. I'm very familiar with his work. He is one of the very, very, very few not in it for the money.
Yeah, also he was pretty upfront on a forum about the costs involved in making the product with a bit of a breakdown as well.
Yes, it's true what you say about the measurements in the digital domain Vs audibility.
It is (relatively) easy to simulate that with extra long cables. Or less than optimal USB host implementations.
For this analysis I will try to instrument the USB bus. But for my prior work, all I care about is what comes out of my DAC and USB adapter, and there, as I mentioned, down to -130 dbFS or so, I don't see such noises. Has anyone else measured otherwise on a high performance DAC? I am not saying it doesn't exist but I have only seen USB dependent noise in cheap sync DACs.
I don't know how to resolve that puzzle, nor will I try.
I just like to characterize what the devices do or don't from design perspective. There seem to be different approaches with one using a USB hub and the other, analog filtering. There will be differences there of value for some people to know. Just want to be clear that while I will be also testing using typical audio measurements, my goal is a circuit analysis at USB level. For sure you can't try to correlate those directly with audibility because what the DAC does with what comes out or doesn't come out of these devices is an unknown.
Thanks. That was a very good read with good info. I hope to go beyond the picture he took though
. On pictures, what he is doing here raises the eyebrow from engineering point of view on such a device:
Thanks. That was a very good read with good info. I hope to go beyond the picture he took though
This device is an analog low-pass filter. A low-pass filter gets rid of energy above certain frequency. That energy must go someplace and that place is the ground. The ground exists inside the computer. When you hook up to it using that long blue USB cable, it represents pretty high impedance at high frequencies and as such, doesn't act much like a ground. Ergo little filtering actually occurs. I suspect the manufacturer does not recommend such use.
Question: does anyone know how you put two of these in "parallel?" The device has only one in and one out. How do you get two of them on the same port???
That was not what I was specifically asking but yet your answer means that you will have to characterise the USB signal as having SI problems - can you do this - can you do USB eye diagrams?
The theory (& measurements show) that the USB protocol running at high speed (125us microframes) has a resultant 8Khz noise spike as a direct result & easily seen on the analogue output. However if you first use a USB converter & output balanced AES/EBU to your DAC, this arrangement may well suppress such common mode noise?
Well, characterising a device is a different issue than running some measurements on it which may or may not be different to the same measurements run on another deviceI don't know how to resolve that puzzle, nor will I try.
As I said, the proposed explanation for what the Regen does is to reduce noise in the PDN (power delivery network) that arises when the USB PHY has to deal with USB signals with lower SI. Given this, logic dictates that this will not be a fixed noise level but will fluctuate in the presence of variable USB signal SI.
