Diy professional DAC & questions on word clock
Hi everybody
I'm a student in sound engineering, and prior was a student in electronics and industrial IT.
I plan to design a full digital audio system, from ADC to DAC. But I still lack knowledge, and I have some questions to ask to you.
My goal is to make a professional system, not an audiophile system.
So here we start!
One of the main problems with digital audio is the jitter of the clock. A DAC could be designed to try to solve this problem, using the well-known topology:
In->Receiver->ASRC->oversampling->FIR ->DAC->IV->analog filter -> out
This is quite complex because we try to cancel the jitter. We have to build a good quality clock inside each element we will use (ie inside the DAC, ADC, and interface). And ASRC is not a "magical chip".
My idea is that we are in the professinal field. So why not buy a good quality word clock and stop using seperate clocks? This is probably the way to the lowest jitter, and keeping prices down - a clock in each element is expensive, if we don't need them, just don't buy them....
I read many topics on transport, I think I'll go with Toslink as jitter on optical links are the easiest to get rid of.
The topology should then be:
In->Receiver->oversampling->FIR->DAC->IV->filter->out.
Then it becomes harder!
Let's use a PLL on the receiver, as I don't want it to add it's own jitter: it should then clock data out at the same rate as the data comes in. I fear of clocking it directly with the word clock, but maybe I'm wrong?
Let's clock the Oversampling and the DAC to the word clock.
What is exactly the frequency given by the word clock? Because it's not the word clock that I need now - it's the bit clock, that depends on the resolution and the oversampling (and of course the sample rate).
How to get this bit clock?
Let's start with these questions, when I'll have solved them I'll go to the next ones
Thank you very much,
Nicolas
Hi everybody
I'm a student in sound engineering, and prior was a student in electronics and industrial IT.
I plan to design a full digital audio system, from ADC to DAC. But I still lack knowledge, and I have some questions to ask to you.
My goal is to make a professional system, not an audiophile system.
So here we start!
One of the main problems with digital audio is the jitter of the clock. A DAC could be designed to try to solve this problem, using the well-known topology:
In->Receiver->ASRC->oversampling->FIR ->DAC->IV->analog filter -> out
This is quite complex because we try to cancel the jitter. We have to build a good quality clock inside each element we will use (ie inside the DAC, ADC, and interface). And ASRC is not a "magical chip".
My idea is that we are in the professinal field. So why not buy a good quality word clock and stop using seperate clocks? This is probably the way to the lowest jitter, and keeping prices down - a clock in each element is expensive, if we don't need them, just don't buy them....
I read many topics on transport, I think I'll go with Toslink as jitter on optical links are the easiest to get rid of.
The topology should then be:
In->Receiver->oversampling->FIR->DAC->IV->filter->out.
Then it becomes harder!
Let's use a PLL on the receiver, as I don't want it to add it's own jitter: it should then clock data out at the same rate as the data comes in. I fear of clocking it directly with the word clock, but maybe I'm wrong?
Let's clock the Oversampling and the DAC to the word clock.
What is exactly the frequency given by the word clock? Because it's not the word clock that I need now - it's the bit clock, that depends on the resolution and the oversampling (and of course the sample rate).
How to get this bit clock?
Let's start with these questions, when I'll have solved them I'll go to the next ones
Thank you very much,
Nicolas