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Review and Measurements of Pro-Ject Pre Box S2 Digital

sonci

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They actually test every single device on an analyzer.
I have bought 2x A30's and a D30 and a DX7.
All had measurement papers in the box, but then again I've had the A30/D30 for a year already before it was popular.

I could probably ABX the D30 and the DX7 given the right tracks and headphones.
I did spend many times AB testing the two of them and there are a few songs that have specifically more details with the DX7 vs the D30. The difference is not huge and you have to listen critically.
The one thing though is that the D30 has more jitter via USB and this is present while the DX7 never has a pop or crack no matter how long you listen.
Also the D30 is slightly warmer sounding vs the DX7. I did this testing by feeding my DX7 or my D30 through the same A30. Later on when I got my O2 amp I did some additional testing feeding my O2 with either the DX7 or D30. The tests weren't blind but as I said there are differences which are easier to identify especially listening back to back given the right tracks.
Additionally the D30 had some things where sometimes male vocals were slightly recessed in things like TV shows.... its very weird and I did extensive testing with this to find that it doesn't always happen.
Thanks for the description. I don't think Jitter is the cause of pops and cracks, maybe that's much worse.
I've never been a fan of the Sabre dac, but it seems the new chips are much better than the old ones, especially for dsd.
 

amirm

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Music1969

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Ah no! I forgot. Sorry about that. It is already in mail to the owner.

I can try it on Topping D50 as that is also a 5 volt device.
No worries. Yeh why not. If/when you get around to it, can you maybe compare SMPS powering the D50 vs USB powerbanks vs linear PSU?
 

Stereo20

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Good evening guys..wonderful forum;
I'm Dan, from Italy.

I am observing this interesting pro-ject dac; in your opinion how does it sound compared to my jlsounds ak4490 with opamp burson?
Thank you so much!
 

Music1969

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Ah no! I forgot. Sorry about that. It is already in mail to the owner.

I can try it on Topping D50 as that is also a 5 volt device.
Hi Armi, are you still planning to do this with the Topping D50?

Cheers
 
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The Optimal Transient filter in this unit, which Pro-Ject recommends as preferable, has some interesting characteristics. First, at first glance it appears to lack an anti-aliasing filter. Here's how a 1kHz waveform, sampled at 44.1kHz, appears on an oscilloscope with the Optimal Transient filter setting:

1 - Optimal Transient.png


Count those steps and you'll see around 44 of them per cycle. The next filter option, Fast Rolloff, looks like this:

2 - Fast Rolloff.png


BUT, with Optimal Transient filter selected, the rolloff at the high end is much earlier than the other filters:

Pro-Ject FR optimal vs fast rolloff.png


So that's weird. Yet it does seem to deliver optimal transients. I moved one sample in a 44.1kHz audio file up high, then recorded the output of this device with that test clip with the various filter settings. But I used 192kHz sampling to record. Optimal Transient to the left, Fast Rolloff to the right:

Optimal Transient vs Fast Rolloff.png


Optimal delivers a narrower, taller spike with less ringing around it. Now, returning to the frequency response, the above graph uses software intended for well-behaved equipment. It shows what happens within the 22.05kHz bandwidth when there's 44.1kHz sampling.

But what if we record a much wider bandwidth of output. Here it is (outputting white noise) with the Fast Rolloff filter:

Pro-Ject Fast Rolloff.png


And here it is with the Optimal Transient filter:

Pro-Ject Opt.png


Thoughts?
 

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Veri

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The Optimal Transient filter in this unit, which Pro-Ject recommends as preferable, has some interesting characteristics. First, at first glance it appears to lack an anti-aliasing filter. Here's how a 1kHz waveform, sampled at 44.1kHz, appears on an oscilloscope with the Optimal Transient filter setting:

View attachment 21559

Count those steps and you'll see around 44 of them per cycle. The next filter option, Fast Rolloff, looks like this:

View attachment 21560

BUT, with Optimal Transient filter selected, the rolloff at the high end is much earlier than the other filters:

View attachment 21561

So that's weird. Yet it does seem to deliver optimal transients. I moved one sample in a 44.1kHz audio file up high, then recorded the output of this device with that test clip with the various filter settings. But I used 192kHz sampling to record. Optimal Transient to the left, Fast Rolloff to the right:

View attachment 21562

Optimal delivers a narrower, taller spike with less ringing around it. Now, returning to the frequency response, the above graph uses software intended for well-behaved equipment. It shows what happens within the 22.05kHz bandwidth when there's 44.1kHz sampling.

But what if we record a much wider bandwidth of output. Here it is (outputting white noise) with the Fast Rolloff filter:

View attachment 21564

And here it is with the Optimal Transient filter:

View attachment 21565

Thoughts?
Optimal Transient is a NOS-like filter, possibly by zero-order hold on the samples. Same as iFi bitperfect.
Possible also same as AKM chip's "super-slow roll-off"
evidence for the AKM filter showing the same stepped/aliased response:
 

Music1969

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The Optimal Transient filter in this unit, which Pro-Ject recommends as preferable, has some interesting characteristics. First, at first glance it appears to lack an anti-aliasing filter. Here's how a 1kHz waveform, sampled at 44.1kHz, appears on an oscilloscope with the Optimal Transient filter setting:

View attachment 21559

Count those steps and you'll see around 44 of them per cycle. The next filter option, Fast Rolloff, looks like this:

View attachment 21560

BUT, with Optimal Transient filter selected, the rolloff at the high end is much earlier than the other filters:

View attachment 21561

So that's weird. Yet it does seem to deliver optimal transients. I moved one sample in a 44.1kHz audio file up high, then recorded the output of this device with that test clip with the various filter settings. But I used 192kHz sampling to record. Optimal Transient to the left, Fast Rolloff to the right:

View attachment 21562

Optimal delivers a narrower, taller spike with less ringing around it. Now, returning to the frequency response, the above graph uses software intended for well-behaved equipment. It shows what happens within the 22.05kHz bandwidth when there's 44.1kHz sampling.

But what if we record a much wider bandwidth of output. Here it is (outputting white noise) with the Fast Rolloff filter:

View attachment 21564

And here it is with the Optimal Transient filter:

View attachment 21565

Thoughts?
HQPlayer's developer has said those filters measure the worst with this DAC.

He recommends "linear fast roll-off" with "distortion compensation enabled".

Do things look better with these two options selected?
 
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HQPlayer's developer has said those filters measure the worst with this DAC.

He recommends "linear fast roll-off" with "distortion compensation enabled".

Do things look better with these two options selected?
Yes, I've used Fast Roll-Off as the comparison measure. All measurements were with distortion compensation enabled.
 

Music1969

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Yes, I've used Fast Roll-Off as the comparison measure. All measurements were with distortion compensation enabled.
To me your fast roll off results look best overall - consistent with what HQPlayer's developer noted too...

Even with the impulse response - if you ask Ayre/Meridian/MQA Ltd which looks more optimal of the two, they might say the 'optimal transients filter' (they lean to minimum phase, slow roll-off)... But if you asked Chord or Benchmark which of those two impulse responses looked better they might have a different answer (they prefer linear phase, i.e. symmetrical filters, fast roll-off...). But they all claim their filtering methods lead to best transient response performance...
 
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Graph Feppar

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I noticed one interesting thing, Amir measurement show the amp have 1.9 ohm impedance while the Russisn site shows 0.1 ohm and then rise to 0.5 ohm at 20 KHz but this is probably becose of the 19 KHz low pass filter.

I think it is becose Amir powered it only through USB and didnt use powerbrick. Maybe with powersupply connected it will have 0.1 ohm output impedance?
 

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