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In Reply to: RE: PS Audio DirectStream DAC - an extremely interesting video. posted by beppe61 on February 14, 2015 at 23:21:58
I suspect that I understand the basis for your excitement - you are hopeful that significantly more satisfying music has been hidden on your CDs these past three decades, and that conversion of all those PCM CDs to DSD is the secret to experiencing that satisfaction. It's the audiophile holy grail of CD playback.I only would caution you to be careful not to substitute hope for a sufficiently long pre-purchase audition. Optimism about the future bringing better sounds drives most of us I suspect. However, I've learned through past purchase decisions to not let a list of features and technologies, nor specifications, nor published reviews, nor brand name, nor overheated marketing talk make my audio purchase decisions. Those factors help inform what I audition, but it is the audition that decides. If I can't audition, then I do not purchase, especially, when it comes to multi-thousand dollar components.
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Ken Newton
Edits: 02/16/15 02/16/15 02/16/15Follow Ups:
Hi and exactly ! I hope just that.
The fact that digital sources sound so different means to me that digital is still relatively unknown, not fully understood.
Jittery signals that sound good ... so why lower the jitter ?
Then there are things that are just unacceptable ... like the pre-ringing in the graph taken from the Stereophile magazine.
This is really weird .. a signal before the music.
Let's say that i am optimistic.
And what is nice is that even cds can be made to sound more musical.
At least this is the promise.
Thanks again.
Kind regards,
bg
Imagine for a moment the "perfect" brick wall filter, one that completely zeroes all content above the cutoff frequency and leaves the amplitude and phase response below cutoff completely unchanged. You can implement this perfect filter by FFTing the whole time series, setting all frequency samples above cutoff to zero, and iFFTing back to the time domain. The result will have pre-ringing. I think it is a natural side effect of band limiting.
You can implement a filter with no pre-ringing and only post-ringing in either the analog or digital domain, but as Ken points out it will have phase distortion.
Here is one more hypothetical to think about, which will probably seem counter-intuitive:
Suppose you start with an analog signal that is band limited so it has no content below fc, where fc < fs/2. Then you put it through an ADC-DAC loop and the reconstruction filter is a linear phase brick wall FIR type with flat response to fc. The output will just be the original signal plus dither noise. The ADC-DAC loop will not have added any ringing. Any ringing present in the output will be due to the band limiting of the original signal prior to conversion. This may seem counter-intuitive but is mathematically true.
Note that the digital test data that produces pre-ringing when put through a DAC is not properly band limited and thus violates the sampling theorem. We're used to seeing DAC measurements in Stereophile and other places which use a perfect digital impulse or digital square wave as the test signal. These are not band limited and are not representative of digital data that came from an ADC. They make it seem like the reconstruction filter adds ringing artifacts to the signal but if the signal is properly band limited in the first place, it does not.
Of course, if you start with a music signal with frequency content > fs/2, then you have to filter the data to band limit it, and the filter will introduce ringing. It could be pre- and or post-ringing depending on the filter type. So I think that putting all the attention on the reconstruction filter is misplaced. The attention should be on the filter at the front end of the process, not the back end.
Also, I agree 100% with Ken that the Achilles' Heel of CD is the requirement for a brick wall filter at the top of the audio band due to the low sample rate. That is something that cannot be fixed on the replay side.
Hi and thanks a lot for the very kind reply
I am afraid this is much beyond my ability to understand.
What i think is that digital cannot be considered "mature", and i refer to the cd format.
It is possible that with the technological advancement better performance could be obtained even from old cds.
This is what interests me most ... i have only cds.
I have to wait and see.
Thanks again.
Kind regards,
bg
I was going to make a similar post.
The problem is the 44 kHz format. It is irretrievably damaged. It was a suitable mid-fi format for the 1980's but is way past technological obsolesce. No competent recording engineer makes new recordings today at the 44 kHz sampling rate. However, before release most productions are artificially lowered in quality to mid fi levels (44/16) or crap levels (AAC or MP3).
Frankly, I could care less how a DAC plays CD quality recordings. I don't ever send this format to my DAC. I always convert it via software to either higher sample rate PCM or to DSD128. If one uses various software programs one can experiment with different conversion processes and different filtering settings without spending money for special hardware. If you convert to DSD, be sure to convert to at least double speed DSD (DSD128) as otherwise there will probably be a noticeable loss of transparency do to the limitations of the DSD64 format.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Yep, the problem is the 44.1k format.
I've messed around with upsampling CDs to higher res PCM in software using different filters, but not upsampling to DSD because I don't have a DSD DAC. Different filters give slightly different flavors, but I haven't been able to do better than the one in my DAC except on mellow jazz music where I think I prefer a filter with a slower roll-off, but not by a wide margin. CD still sounds like CD. You can't undo the damage of the brick wall filter used when recording or downsampling.
Yes, that's the pre-ringing impulse response of a linear phase brickwall FIR filter. It's the pre-ringing itself which renders the filter linear phase even though it features a brickwall cutoff slope. It's often pointed out that no analog filter (or nature, herself) exhibits pre-ringing phenomena. Which is true. However, what also is true is that no analog filter can provide a brickwall cutoff yet be linear phase.
I used to strongly suspect that the pre-ringing was repsonsible for much of the disappointing sound quality of CD replay. After extensive experimentation with my own homebrew DACs I now don't think so. I now think it more likely that, at least in part, the often disappointing sound of CD replay has to do with poor transient response implications of CD's requirement for a brickwall filter cutoff slope, which, itself, is neccessitated by the CD standard where the Nyquist frequency is very close to enough to the signal bandwidth.
As I indicated earlier, their rarely is a consumer's check list of features and technology which when followed delivers satisfying replay to all ears.
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Ken Newton
Hi and thanks a lot for the very helpful reply.
I think i will wait patient for some development.
I have made only side moves recently ... no real improvement.
I know that the main problem is not the system downstream the source, because i try a turntable and the sound was decent, musical and enjoyable.
I think i will wait, read here and see ... and listen of course.
Thanks again.
Kind regards,
bg
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