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In Reply to: 24 bit and anti-jitter circuit right?
The crystal cs4397 src in the p-3a converts 16 bit/44.1kHz to 24 bit 96kHz. The p-1a does the same thing, but I believe with a proprietary algorithm. I thought the only reason to use the p-1a was if you intend to use speaker/room correction.steve
Follow Ups:
I think it is only capable of upsampling to 96k. Thought in the P-1A, one chip upsamples, and the other DSP chip converts to 24 bit.
The reason to use them both is that they work in synergy together for the best impact. The P-3A upsamples to 96khz and uses dither to achieve the 24-bits. The P-1A does an excellent job of jitter reduction first of all, secondly, it extends the wordlenth to 24-bits using a proprietary algorithm that has been years and thousands of computer code in the writing. The result is a FAR superior means of producing 24-bit resolution.When used with the P-3A then, while the P-1A is also able to upsample to 96khz, it sounds best when the P-1A is set to output 24/44.1 and lets the P-3A do the final 96khz upsampling.
Both units I believe are also equipped with an I2S input and a future optional software upgrade to allow these units to be used with 24/192 date - e.g. DVD-A, SACD, etc...now all we need is a Universal Transport.
Now enter speaker correction. I have only heard the speaker correction and not the room correction yet, but the speaker correction completely blew me away. I will be writing a lengthy report of the fun I had at CES and what I liked there, but for now I will simply say that when Peter turned the speaker correction off and then back on again, it was like someone turned the lights on...it is THAT GOOD.
I hope this clears things up a bit and if I am mistaken about any of what I have said, I hope someone will correct me.
Dan W.
What would otherwise be the 24-bit dithering in the P-3A (via the Crystal chip) has been defeated, or bypassed, or whatever you want to call it, by the Perpetual designers.Therefore, you need the P-1A with this combo to get to the simulated 24 bit word length.
Also, to an earlier question about why you need both the 1-A and 3-A, don't forget that the 1A offers astoundingly good jitter reduction, the benefits of which are incontrovertable, and much discussed in this forum. Even if you don't utilize the resolution enhancement of the P-1A, you receive sonic benefits from the jitter reduction.
Best regards, Paul
The p-3a does use 24 bit when sample rate converting to 96k. Still doesn't make sense to use both devices unless speaker or room correction is used, IMO. Your comments about the development and performance of the p-1a also apply to the p-3a!steve
Steve,I think you're wrong here. Stand-alone, the P-3A will upsample to 96kHz, but merely adds dither to the 16-bit data to create a 24-bit signal. The P-1A can do that, but it also (and separately) can generate interpolated 24-bit signals, using DSPs and proprietary software not included in the P-3A DAC.
P-Tech and most reviewers, including Dan W here, suggest running the P-1A to do only this interpolation to 24-bits, outputting a 44.1 kHz 24-bit signal to the P-3A, which then upsamples that input to 96 kHz. It is also possible to have the P-1A do both , to output interpolated 24-bit signals to the P-3A at 96 kHz, which should then be set to not upsample, but all I've read indicates that it is better to have the P-1A increase the word length and the P-3A upsample.
So the P-1A brings something to the party in addition to jitter reduction (now) and speaker + room correction (future).
BTW, the review of three DACs in the current Secrets of High Fidelity and Home Theater describes using the P-1A in this manner to drive the Link and Bel Canto DAC-1.
cooney
The crystal sample rate convertor chip in the p-3a maintains 24 bit precision in its calculations while converting the sample rate tp 96kHz using interpolation.I believe some of the reviews I've read also misunderstand what's going on or at least how to explain it.
steve
I think you are still missing the point: . there is a difference in how the P-3A (as well as most other upsampling DACs) and the P-1A approach creating a 24-bit signal from 16-bit input.While, as you indicate, the Crystal sample rate converter chip in the P-3A "maintains 24 bit precision in its calculations," it does this by adding dither to the signal, which is different from creating a 24-bit signal by interpolation using DSP, which can be done by the P-1A but not by the P-3A. . Please note, I'm not saying better, just different, as I've not heard this yet. . (I note, however, that Dan Wright and most of the others posting here who have listened to both feel that the P-1A's interpolated signal is preferable; . some users, as indicated earlier in this thread, are not so sure.)
In the recent review of the P-1A/P-3A in SoundStage! , Doug Blackburn quotes one of the P-Tech founders as follows, which is one of the most concise explanations I've seen of this distinction:
"Peter Madnick clarifies the operation of the P-3A and other so-called 24/96 DACs and 24/96 outboard processors this way: . The P-3A does not interpolate 16-20-bit data to 24-bit data -- nor does any 24/96 DAC (e.g., the Bel Canto DAC1) or add-on 24/96 external device (e.g., Assemblage D2D-1). . All of these products, so far, will output 24-bit data via dithering of the 16-bit input data. . This results in data that has roughly 17 bits of equivalent resolution within a 24-bit datastream. . The P-3A and other 24/96 products do upsample, for example, from 44.1kHz to 96kHz if you select that mode. . People tend to assume that 24/96 products that advertise upsampling and/or interpolation actually convert 16/44.1 data to full 24/96 resolution, which is not accurate. . To actually get 24-bit data in a 24-bit datastream, you must use digital signal processing (DSP), which is included in the P-1A and is referred to as "Resolution Enhancement" in the P-1A's user manual."
Hope this helps explain the distinction between the two processes, adding 8 bits of dither versus interpolation of 24-bit data by software running on DSP chips.
cooney
Thanks for the notes cooney :)Usually when discussing sample rate conversion 'interpolation' refers to the extra samples created during upsampling. Precision is used to describe the 'resolution' of the samples after processing. How the value of the samples are calculated is the difference between the 2 PT units, and that is understood.
steve
Hi cooney,No, it only adds to the confusion because it's not quite accurate. The CS8420 does do interpolation, as all up/oversampling chips do - in fact interpolation is implicit in up/oversampling. I'd be amazed if the CS8420 didn't pass 24 bit data (without dither), as it takes more effort and expense to dither the signal rather than pass the expanded wordlength to the output. It just wouldn't make sense.
Here's what PT's own literature says on the subject:
"The CS8420 device actually has a 24-Bit data path to its
outputs, with some dithering options to reduce the
word length. We are not using the CS8420 device’s
dithering option, but instead use our own proprietary
“adaptive dithering algorithm” in the DSP. For a
44.1K sample CD source, the CS8420 device is
passing 24 bits, which essentially track the 16-Bit
source signal into its new output sample positions."So, in the P-1A the CS8420 is passing 24 bits, but they are not using it's dithering options.
What the P-1A does that no other DACs do is what PT call resolution enhancement. This isn't interpolation in the sense that the term is usually used in, it's a process of estimating the value of the original data using psycho-achoustic techniques. It may work very well, but can we call any value that is the result of "estimation" (PTs own term) True 24 bit data?
Note: plenty of DACs are running at 24 bits without a bit of dither in sight. Also, all up/oversampling chips are DSP chips.
Daniel Espley
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