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In Reply to: RE: PS Audio DirectStream DAC - an extremely interesting video. posted by oldmkvi on February 14, 2015 at 01:21:59
Hi and thanks a lot for the very valuable reply. So it really works.
From what i understand the nice thing with DSD is that, high rez aside, it allows for the use of analog filters, supposedly better sounding than digital ones.
The fact that DSD seems more like music for me is quite intriguing.
I hate and love digital ... i hate it for its sound, but being lazy i love it for its convenience (this is great !).
I think we are on the verge of a revolution in digital audio.
Unfortunately i have already invested too much on pcm ...
Thanks again.
Kind regards,
bg
Follow Ups:
NOS dacs like my metrum Hex have no digital or analog filters and use ladder dacs to recreate the signal from redbook. Isn't DSD really just 1 bit PCM with massive oversampling? I have heard it described this way
Alan
Hi and thanks a lot for the very interesting explanation
I am very ignorant on the subject but i do a simple reasoning
There are dacs where is possible to change the digital filter
The sound changes always remarkably ... so the digital filters have a huge impact on sound.
And no sound with digital filter is natural ...
So i think that the real issue is the filtering.
DSD, high rez aside, allows for the use of analog filters that for their analog nature have no artifacts. This is the real strong point of DSD more than the high rez.
I do not know by the way if all DSD dacs have analog filters, but i think they should have because it makes the difference.
To end ... i think i will be very soon looking for a pcm to dsd dac with analog filters
I am afraid it will be both great sounding and very expensive
But i trust completely Mr. McGowan's words ... if he says that the sound is splendidly natural and musical i tend to believe him completely.
He also states that it is much superior to the sound of their best pcm dac ... already a superlative unit from what i have read here and there.
I am completely convinced that this is not marketing hype but more a revolution in digital audio.
I am sure very soon we will see cheap chips doing the conversion from pcm to dsd ... after those chips an analogue filter will cost next to nothing.
Too good to be true ? we will see soon
Thanks again.
Kind regards,
bg
Edits: 02/14/15 02/14/15 02/14/15 02/14/15 02/14/15
You might like to start your research here, for example .
Big J
"... only a very few individuals understand as yet that personal salvation is a contradiction in terms."
"The sound changes always remarkably ... so the digital filters have a huge impact on sound.
And no sound with digital filter is natural ...
So i think that the real issue is the filtering."That depends on the digital filter.
"DSD, high rez aside, allows for the use of analog filters that for their analog nature have no artifacts. This is the real strong point of DSD more than the high rez."
The simplicity of the analog filter only depends on the sample rate, and has nothing to do with whether the DAC coding is single bit DSD or multibit PCM. If both are run at the same sample rate then their analog filter implementations can be identicle
"I am afraid it will be both great sounding and very expensive...But i trust completely Mr. McGowan's words ... if he says that the sound is splendidly natural and musical i tend to believe him completely...He also states that it is much superior to the sound of their best pcm dac ... already a superlative unit from what i have read here and there.
I am completely convinced that this is not marketing hype but more a revolution in digital audio."Heavens, why would you simply take his word for how you would percieve the sound? Mr McGowen has a financial dog in this fight. His opinion will naturally be biased, whether he consciously realizes it or not. That fact alone alone renders his statement suspect.
"I am sure very soon we will see cheap chips doing the conversion from pcm to DSD"
I wouldn't bet money on that.
_
Ken Newton
Edits: 02/14/15 02/14/15 02/14/15
Hi and thanks for the very interesting reply
So in the end you think it is mostly marketing, a commercial display.
Honestly i cannot be sure of what he says
But if he is right i think we will see many products with similar solutions from other manufacturers.
Anyway the few reviews in the net are very positive about the mentioned dac.
I can wait for now and see.
Thanks again.
Kind regards,
bg
I don't know of it's mostly marketing hype, but it surely is partially so. For the record, I'm not denigrating the product, which I have not heard, nor the man, whom I have not met. I'm only reinforcing the old audio truism that one must listen to the product, not to it's designer or it's seller.
I wish it were possible for consumers to reliably select the best audio components for their particular ears and listening biases based only upon specifications, or upon some list of certain features or technologies, or on the word of some particular person. That would very much help widen the consumer appeal of high fidelity audio in my opinion. In my experience, however, such isn't yet possible.
_
Ken Newton
Hi and i understand your point of view
I agree, obviously, about the importance of listening the system.
Sometimes is not that easy.
But more than the specific product i am intrigued and a little excited about the technology behind it.
First this would be another evidence of the nasty effects of digital filtering on the sound. Removing them increase the musical pleasure a lot.
Then the statement that even the so badly judged cd format can give a very pleasant sound.
There is a passage when the speaker says something like ... you really do not know what there actually is on your cds !!!
Amazing.
I am expecting other manufactures to jump on the pcm to dsd upsampling with analog filtering.
Thanks again.
Kind regards,
bg
Edits: 02/14/15
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.
_
Ken Newton
Edits: 02/16/15 02/16/15 02/16/15
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.
_
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
/
"NOS dacs like my metrum Hex have no digital or analog filters and use ladder dacs to recreate the signal from redbook."
No way. It has to have an analog "reconstruction filter" to block all the aliasing energy above Fs/2 or they will likely wreak havoc with your amplifiers and speakers. And maybe even ears... It's really within the filter that the original signal is "recreated".
Rick
No way. It has to have an analog "reconstruction filter" to block all the aliasing energy above Fs/2 or they will likely wreak havoc with your amplifiers and speakers. And maybe even ears... It's really within the filter that the original signal is "recreated".
Most of the NOS DACs have a zero order hold, at least to the extent that there are no logic glitches in the output signal. This greatly reduces the amplitude of the high frequency images. It also provides a high frequency roll-off below Fs/2, thereby diminishing high frequency response, a potentially useful "tone control" effect for systems that are otherwise too bright. One can debate whether the ZOH is an analog filter or a digital filter, but a filter it most certainly is.
Without this ZOH filter one gets a stream of Dirac impulses and if these are not filtered there may be serious high frequency energy to disrupt sensitive drivers such as tweeters.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
My Hex has no analog filter as do most NOS dacs. Here is a quote from Audio Notes website
"To complete the pure digital to analogue design of the DAC 4.1 the digital board has no analog filtering (analog filtering has been totally removed). We have found having analog filtering in the signal path has a marked detrimental effect on sound quailty. If you are looking for digital sound reproduction with no digital artifacts and smooth as velvet output with no fatigue then the DAC 4.1 is the kit for you!"
Alan
"My Hex has no analog filter as do most NOS dacs."
Odd, it should, it's simply part of a properly implemented sampling system. Maybe it has a low bandwidth stage that is one in effect but called something else.
Thanks for the info, Rick
The lack of an effective or an specific analog image rejection filter is no longer that uncommon. The frequencies that such a filter would remove are ultrasonic, which means that the without the image filter they still are eventually low pass filtered by the interconnects, the amplification chain, the loudspeakers and, finally, the human ear. Leaving the ultrasonic images unfiltered at the DAC analog output might, however, cause intermodulation and/or RF rectification problems in the active amplification chain. The general rational given for why this filter is omitted is that it makes the DAC sound better.
_
Ken Newton
Audio Note's decision to remove the analog filters began with a project transcribing Russian opera 78s. They were pretty darn noisy, so a low order, top parts quality filter was applied to quiet things down. They were startled to hear that not only did it reduce noise, but it sucked all the life out of the music.
This prompted an "Aha" - really an "oh shit!" - moment when they considered what was likely happening in the DACs. Once they worked out a filter less design, I had the opportunity to perform a large number of "filterectomies" on DACs sent in my owners of filtered DACs. I listened to all of the befor and after and I can tell you the difference was far from subtle. Clearer, cleaner, more detail, sparkle, life, regardless of the music played.
Keep your ears and your mind open.
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