NorthSky
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Yes, as measured from people's ears. As for real graphs I'm sure they are around....before and after. Let me locate them for you Mike...
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What is 'incompetent digital' ?
- Thread starter Opus111
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Yes, as measured from people's ears. As for real graphs I'm sure they are around....before and after. Let me locate them for you Mike...
Mivera
Major Contributor
I'm trying to get find a pattern of what "musicality" looks like on paper. But I'm thinking it might take buying an AP machine like Amir's to play around with to figure it out.
- Thread Starter
- #164
If you do buy an AP try out the multitone testing option, it holds more promise than simple THD+N measurements.
Here's a (very old) primer on multitone measurements on amplifiers - https://www.researchgate.net/publication/271501230_A_new_distortion_measurement
Here's a (very old) primer on multitone measurements on amplifiers - https://www.researchgate.net/publication/271501230_A_new_distortion_measurement
We don't know if he heard anything. We need to establish that before we go and try to find a measurement to match it.
NorthSky
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I just had a momentary lapse of reason. It's raining real hard here right now with heavy winds...power can go out any second...
Mivera
Major Contributor
If I buy one I'll be trying every feature out that's for sure. Which one do you have Amir? For me the apx515 would be enough but I wish it had better specs for THD+N. To get the models with the better specs you need to buy the ones with a pile of I/O I would never use.
It is trivial to read fidelity differences into anything. In countless situations I have thought I made a change, heard a difference, could explain it, and then realize I had not made any changes!
Real example. I had my two sons over to teach them acoustic science. I measure the room, find a peak in low frequencies and dial up a filter to knock it down. Do this a couple of times and my sons both nod in agreement. I do it again and ask them if they heard how much tighter the bass was. And how the boominess is gone. This time they reluctantly say yes. I look down and I notice that I had never turned on the filter! It was a checkbox in the UI and my hand has just moved a few pixels over and hence, was not changing the checkbox.
I can tell you countless stories like this. It is routine, and completely predictable that we read changes into how something sounds whether the sound actually changed or not. Sitting there and messing with the circuit ups this probability easily to surety.
The above is why I always test my results blind.
But no, I don't know that he did not hear anything. I am saying that we don't know if he heard it.
Mivera
Major Contributor
Stay safe Bob!
- Thread Starter
- #171
With a very restrictive definition (not saying its a wrong one, mind) of 'know' then yeah I agree we don't know what he heard. Einstein himself said 'the only source of knowledge is experience'. But if we want to postulate what he heard was due to placebo then that to me looks to be a non-falsifiable hypothesis.
I have the last generation system (cascade sys-2522). The newer one (apx555) with the best spec nearly $30K. The lower costs ones they offer have worse specs.
I don't know that if I want to do this yet but let me know if you are interested in buying mine as I might upgrade to the new one.
Mivera
Major Contributor
Depends on the implementation. So far there's been many generations of USB interface implementations. The most basic is like the Amanero with no galvanic isolation, and powered by the USB bus. This is the worst as it's powered by dirty power and has nothing to isolate the noise from the USB bus from getting into the DAC. let alone the mediocre clocks. Then along came galvanic isolation. But it's no free lunch either. The galvanic isolators, although they isolate the grounds, they also add jitter themselves. So if you power the USB interface from a clean power source, and connect a low noise streamer up to it, it can actually sound better without the galvanic isolation. But then it was discovered that you can re-clock with flip flops after the galvanic isolation, power the USB interface with ultra clean power after the isolators, and the jitter is reduced to levels lower than anything before. So not only do you get the low jitter, you also get the isolation. The only sacrifice is you must use clocks of double the frequency as the flip flop halves the frequency.
But that's not the only issue with USB interfaces. The clocking scheme itself needs to be considered. USB interfaces use 2 clocks for Async operation. The 1st clock clocks the incoming signal, and then there's an FPGA, or Async USB chip such as XMOS or Cmedia that buffers the data into RAM and re-clocks the data with clock# 2. But then the DAC chip has it's own master clock, so the data has to be clocked again by it. This is a poor way to do things. The better way is to just use very good clocks in the USB interface, and syncronously slave the DAC chip to clock # 2 of the USB interface. This is the lowest jitter way to do things. However you need to make sure the DAC chip is located in close proximity to the USB clocks, because the further the clock has to travel, the more jitter is introduced.
The DAC in the PD2 uses the very best of all the strategies I mentioned above for the USB. It had undergone several prototypes to get to this point and I had tested some as well. This is by far the best yet, and it seems to really be immune to variances in the connected computer finally.
You can see how close the DAC chip is to the USB clocks in the photo. Building the USB interface onto another board you wouldn't be able to achieve jitter this low. And using a fancy high end external clock, good luck getting jitter this low by the time it makes it to the DAC chip. Those are made for the pro sound world when several devices need to be clocked in sync. However some manufactures purposely make the internal clocks in their DAC's poor, so they can sell you an external clock and you actually hear a difference.
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Mivera
Major Contributor
How much?
- Thread Starter
- #175
Are the analog filter stages on a daughter-board connected above the DAC via J12?
Mivera
Major Contributor
Yes. Another modular board plugs onto the top of it. This way when a new DAC comes out, you just have to swap the 1 board. It also isolates the sections from each other.
- Thread Starter
- #177
I'd be a little concerned about capacitive coupling of noise to those traces between boards. Are they running over the power plane or are there gaps in the plane to minimize parasitic capacitance? Admittedly they're balanced, which does help quite a lot.
Mivera
Major Contributor
Ask Sonny. Didn't seem to be a whole lot of distortion in his posted measurement.When I plug it into my power amps, crank the gain stages in the preamp to +12dBFS, and put my ear to my speakers, it sounds like the system is off. So for me the noise isn't an issue, but we will see if Sonny posts the noise floor measurements.
Mivera
Major Contributor
Here's the current board, however he's working on a new one and anyone who buys a PD2 before it's ready will get the new board upgrade for free.
I already mentioned the difference between the Sabre and AKM chips in the PD2 thread and why the AK4490 was used instead of the Sabre.
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