Chord Qutest

[opus101]

9 hours ago, barrows said:

In the I2S data there are only two things, the data, and the jitter.

 

Since the I2S isn't perfectly isolated, you also have a commonly-overlooked third aspect to consider - common-mode noise currents in the ground wire.

 

Note - these ground currents are by no means a problem for the digital circuitry, they're way below the level needed to corrupt data. But they end up corrupting the analog signal in many cases.

[opus101]

6 hours ago, barrows said:

Not sure what you mean?

 

I was talking about I2S data - there are four wires, three data and a ground. Perhaps I misconstrued your context as you seem to be talking about USB transmission, not I2S transmission.

[opus101]

2 minutes ago, barrows said:

 But the ground from the USB receiver is isolated, that is the point.

 

But no isolation is perfect - you'll have some capacitance forming a high pass filter for noise currents. That's why I said 'since the I2S isn't perfectly isolated'. Practical isolation typically has a few pF of capacitance.

[opus101]

8 hours ago, barrows said:

I never suggested the isolation is 100% perfect, and I have mentioned some capacitive coupling is likely.  That is no reason to not use an isolated USB interface though.

 

Right, but I was only talking about I2S, you said you were too. So back to my original statement, you omitted the small matter (and it certainly is small, but not insignificantly so) of the common-mode noise through the I2S connection.