It is not often in audio that we can prove something mathematically. Turns on in the case of clock jitter/noise in DACs, we can.
Let's say I feed the DAC a simple sine wave. The output in an idea case then would be Y = sin(t) with t = time.
t is determined by the DAC clock which in the above is assumed to be perfect.
Let's make "t" imperfect by adding noise, deterministic changes, etc. That change will have its own function. Let's call that j(t).
Now our equation for what comes out of the DAC becomes:
Y = sin(t + j(t))
This is obviously different from sin(t).
What this says is that mere fact of feeding a DAC a sine wave, allows the output to change with distortions of the clock (j(t)). It has to. It has no choice mathematically.
Of course you all have seen these outcomes. That no matter how good DACs are, no matter how we feed them, we are able to easily see differences in implementations in the
analog output of the DAC.
So the theory Mike has that you cannot use an audio analyzer is busted.
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There is another important bit here. An audio analyzer is not used always to find out what is improved. It is used often to figure out what is screwed up!
Take a look at this diagram from one of my earlier articles which showed that mere changing from HDMI to S/PDIF (bits are bits) made the analog output of DACs completely different:
http://audiosciencereview.com/forum/index.php?threads/a-deep-dive-into-hdmi-audio-performance.56/
We dealt with the clock variations in part one of this post. But there is also a reference voltage that gets divided down to create the output. If you so much as breath on that, you also change the output of the DAC.
If again we fed the DAC a sine wave, and modeled the reference voltage as ref(t), then the output of our DAC becomes:
Y = sin(t + j(t)) * ref(t)
Again, this is different from sin(t) and can easily be measured with a simple sine wave.
High performance DACs from top companies with real engineering expertise go out of their way to minimize j(t) and ref(t). They confirm that with audio measurements.
The DIY companies like we are dealing with this go buy an expensive parts and stick them in DAC and call it done.
They never confirm if they have actually done things that screwed up the output of the DAC!
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Of course I come along, measure them for the first time and the ugly bits show up which they are seeing for the first time.
So don't tell me you don't use an audio analyzer because it doesn't show audible improvements. Tell me that have used one to make sure you have not screwed up anything.
