|
Computer Audio Asylum Music servers and other computer based digital audio technologies. |
|
|
|
Computer Audio Asylum Music servers and other computer based digital audio technologies. |
|
In Reply to: RE: How close to vinyl quality can we get with PCM digital using a computer at home? posted by John Swenson on December 26, 2009 at 06:32:00:
"The big revelation came when I tried my first NOS DAC. WOW, this was a completely different perspective on digital sound. The sense of 3D space you are talking about was there in spades. But on some music it sounded 'grainy' and 'dirty'."You're hearing the HF modulation, which becomes apparent during complex music passages...........
"With brickwall digital filters I had clean sound but it sounded 'truncated' somehow squished and lifeless."
The time response is compromised. In most cases, the music sounds "boring".......
"With NOS it was full and alive but dirty sounding. The LP hit the middle where it was full and alive without being dirty or grainy at all. My goal has been to achieve this with digital."
That is exactly what I've been trying to achieve............
"This ranged over many different DAC chips, types of I/V conversion, output stages and of course a lot of work on jitter. These all improve things immensely, but that previously mentioned dichotomy between full,dirty and squished,clean was always still there."
You've hit on what I called the "time smear/modulation" tradeoff..... NOS playback will have the best time response, but the HF modulation from "nulls" (sampling a waveform near the zero point) causes that "grainy" character you alluded to.
My favorite type of filtering is "time resolute" where some modulation is still present, but there's less "smear" in the time response. Even more ideally, the filter is "minimum phase" where the post ringing is longer than the pre-ringing, which IMO is truer to most music signals than "linear phase" filtering, whose pre and post ringing are the same.
"I did a lot of playing with different digital filters and started making my own. What I have found is that once you get the rest done well (not even perfect, just well) such as IV conversion, jitter, output stage, PS etc the digital filter or lack thereof becomes THE biggest area affecting the sound."
I've been saying that for a long time, but only recently, is there some focus on the digital filter, and attempts to optimize it.
"I have found that most commercially available digital filters in chip form (either builtin to the DAC chip or as external chips) (NOT all but MOST) are seriously flawed. In order to cut costs they are implemented as cascaded smaller filters, this really seriously mucks up sound. If you implement different filter functions but do it using such a cascaded architecture, no wonder people have a hard time choosing the best filter."
There are so many variables, including jitter, various oversample/upsample rates, asynchronous conversion (which I think is a "technology" that should have never seen the light of day), system synergy, RFI issues, etc. .......
Agree totally about the chip-based filters..... The vast majority of digital playback utilized these chips, and IMO has been the weak link of the digital audio chain.
"The filters I have implemented my self don't so this (as is true for several high end equipment that implements their own filters), for me at least its much easier to hear differences between filters functions when not using cascaded filters."
So you're constructing filters from the ground up? If so, you could run a niche business with this, since your only competition would be the hideously-expensive MSB Technology Platinum III series.......
"Even when making my own filters I have not found one yet that I really like for redbook, the format is just too mucked up, the sample rate is just too close to human hearing to come up with a universal 'this is the best way to do it' method."
Half the problem here is the A/D conversion methods would make a single-filter DAC solution next to impossible......... (The A/D filtering would have to be "standardized" in order for this to happen.)
"There are various compromises that can be made in that space between full,dirty and squished,clean but I have yet to find one that gives the best of both."
The tradeoff I alluded to...... You really won't be able to get both, to the fullest degree....... The key is minimizing each effect.........
"It CAN be done with higher sampling rates!!"
Not really..... Once you go over 8x, anything above that only reduces further need for post-filtering.
"BUT just the fact of using higher rates does not guarantee its automatically going to be perfect."
It also increase RFI.........
"Many of the higher sampling rate implementations out there today STILL use improperly implemented digital filters."
Aside from the sample rates, they're basically the exact same filters.......
"You still have to carefully choose the filter implementation, but here I think it is possible to get a filter that gives full, alive, clean and smooth all at the same time."
I think the higher sample rates won't achieve this...... Maybe you will eventually prove me wrong..........
"This is an area that I think the high end really needs to focus on. So far most of the high res implementations I have seen have just been relying on the chip manufacturers implementation of the high sample rate filter."
High rez doesn't even *need* sample rate filters. The "Fs/2" is far enough away from the audio band to implement purely analog filtering..... Under ideal circumstances, the "tradeoff" should be cured by high-rez digital playback. Too bad I've yet to hear a listenable implementation...........
"I have yet to hear one that is optimum. The brain power in the high end has been focusing on trying to come up with something that sounds semi decent with redbook, which I don't think we are ever going to get perfected. I think its time to start putting some brain power on doing high res really right."
Proabably the case...... Some of the best filtering for CD playback was devised in its early days. Put a good output stage on an early 1990s vintage Magnavox or Marantz 5-disc CD changer, and I think it will perform as well as anything short of a Prism DA-2.......
"Some people try and get around the above problems by using upsampling software where they can hopefully get a better implemented filter, unfortunately its still going through the filter in the chip, you are back in cascaded filter land, its never going to sound as good as a single properly implemented filter."
You may have a point here...... I was shocked and disappointed to find out a lot of high-rez playback is still digitally filtered...... And if the upsampling is "asynchronous" (CD playback upsampled to 24/96 or 24/192), that in itself is a signal-mangling compromise.
"The net result of all this is that it if you are willing to go with high sampling rate AND get a really good high sample rate implementation that doesn't muck something up somewhere along the way you CAN get sound that does what you want, that can sound as good as vinyl."
If the RFI problem could be addressed, I'd agree with you, but higher rates mean higher RFI...... The ideal oversampling rate IMO is 4x !!!
"Doing it from redbook is another proposition. I don't think its actually possible to do, you can get pretty darn close, but unfortunately its a tradeoff game and everybody is going to want a slightly different tradeoff. AND just to make it fun that tradeoff is going to be somewhat recording specific."
You actually mentioned "tradeoff", that's exactly what it is......
Aside from your thought that higher oversample rates might fix the problem, you have this digital filter thing nailed...... Maybe the first individual I've encountered on AA to do so.
Edits: 12/26/09
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- You're On the Right Track........ (With a Minor Quibble) - Todd Krieger 22:49:58 12/26/09 (2)
- RE: You're On the Right Track........ (With a Minor Quibble) - John Swenson 02:31:57 12/27/09 (0)
- RE: You're On the Right Track-audioengr please note - fmak 23:08:10 12/26/09 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
