Sunday, 7 July 2013

MUSINGS: Is CD sound quality (16/44 PCM) good enough?

According to some... CD sound quality is inadequate.

In the comments to a previous post, Fabio Zolli asked:

I would like to ask your opinion about high resolution audio files like 96/24 or 192/24 (I know it's off topic but I didn't know where to post). I think there isn't a really audible improvement among standard 44/16, taking into account also your mp3 test. Thanks for your attention.

Thanks for the note Fabio.

The MP3 test shows that even if we do hear a difference, at the level of quality tested (~320kbps MP3), without comparing the "studio master" sound, it's virtually impossible to know which is better/more accurate. Amazing given just how much data is being thrown out by MP3 encoding!

Personally, up to now I have not been able to ABX a difference between properly dithered 16/44 and the 24/96 source. Others have also done some fantastic testing around this like Mitchco at Computer Audiophile with different test methodologies.

It has been 30 years since the introduction of the CD (PCM 16/44) standard for mass consumption. The fact that we have not seen good controlled tests to show that 16/44 is somehow "lacking" (when listening to music at normal volumes) compared to 24/96+ or SACD tells me that 16/44 is most likely good for any circumstance. Much debate for example was sparked in 2007 by Meyer & Moran when they published their report based on work with the Boston Audio Society when listeners could not detect a significant difference between hi-res (DVD-A and SACD) analogue output versus the output from a 16/44 A/D/A loop.

Knowing the above, reading stuff like this should make an unsuspecting audiophile wonder why the inferiority of 16/44 wasn't proven ages ago! The author writes: "For me its clear that 24/96, 24/192 and DSD are superior to 16/44.1 in many meaningful ways..." Really?

The only rational issue I have come across "against" the 44kHz sampling rate is that with older DACs, the Nyquist frequency at 22kHz is too close to the potentially audible 20kHz upper range and the steep "brickwall" filter may cause audible effects. But this issue was addressed with upsampling and slower roll-off filters long ago (I know... yet another contentious issue for some).

Admittedly, I will seek out 24/96 audio for favored albums and rip my SACDs as 24/88. My rationale's simple... Since storage is cheap these days, I consider doing this as reasonable "insurance" to guarantee that everything that science tells us is humanly audible is captured in the digital sampling with plenty of headroom above 20kHz. I believe this is a reasonable price to pay in terms of storage even if I do not ultimately get an audible benefit because my ears aren't good enough for the task (like one pays for insurance never knowing if it's actually needed). Furthermore, objectively, all my DACs seem to be optimal at these 2x sampling rates as well showing nice frequency extension and excellent dynamic range measurements.

As for 24/192...  Christopher "Monty" Montgomery at xiph.org has written an excellent review of this topic including examples of how this could be detrimental to sound quality (like intermodulation distortion which also can be shown with 24/96). Likewise, Dan Lavry has written about the technical issues of 24/192 in his whitepapers like this one.

Personally, I have yet to find music I thought could benefit from this high sampling rate (how many microphones can even accurately record >40kHz?). Even though storage is cheap, I'm not convinced that there's anything to be gained going from 96kHz to 192kHz theoretically or otherwise. The cost-benefit ratio is hard to justify when benefit seems to be zero! (BTW I have come across some albums like Carmina Celtica from Canty off the Linn download site at 24/192 with unusually high noise level above 45kHz which I suspect could create some very nasty intermodulation distortion if not properly filtered.)

Bottom line:
I'm happy with 16/44 if the music is well recorded and mastered. For my favorite tunes, I'll go for 24/88 or 24/96 if available to "ensure" that I'm not missing something. To date, I have happily downsampled many 24/192 albums to 24/96 (or 24/176 to 24/88) without any reason to think that I'm somehow "missing out" (rather than gaining space for more music!). As for DSD, I only have a few albums verified to be sourced from an original DSD recording.

As many others have commented before, the main "enemy" to good sound these days is not about the audio format - yes, even the much-maligned-by-audiophiles MP3 can sound excellent if the underlying content is good. Rather, the way the album was recorded and mastered is more important. For example, the loudness war has caused more damage to sound quality than we can ever gain going from 16/44 to any high-resolution format. I believe sound quality "evangelists" like Neil Young would do well to "wage heavy peace" on that silly "war" and in the process stay relevant.

Feel free to leave me a note especially if there are good reasons to consider keeping 24/192 music on my server system! :-)

One more thing... There is one situation where you'd definitely want to either upsample or run a higher sampling rate - if you're using a NOS DAC. However, this is more to do with reducing aliasing distortion in the audible spectrum.

Musical selection tonight: Going to have a listen to k.d. lang's IngĂ©nue (1992) again... It's been awhile!

11 comments:

  1. It comforts me to hear someone who thinks so. I've done a lot of tests, both abx and normal listenings, using 24/96 or even 24/192 but with no success, no audible difference.
    Keep up with this wonderful blog!

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  2. Yep it's confirmed I'm not getting crazy, I also didn't notice any diferences.

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    1. :-) Not crazy... I just hope you, Fabio, and myself are not deaf. :-)

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  3. The differences between different masters out there for the different distributions is FAR greater than the differences between 16/44 and 384/32 though arguably the latter can describe background noise better than 16/44 can.

    A simple glance at DR database tells enough IMO.

    Higher resolution during the whole recording process IS very beneficial though for very obvious reasons.

    At the same time I can appreciate the thought that some would like to hear recordings in their original resolution when available... if it were only to easy the mind.
    An eased mind can 'enhance' a musical experience.

    Technically a sound decision (no re-sampling that is) but the audible improvements, however, are debatable.
    Arguably it is technically better not to down-sample or converted to other sample rates.

    Up-sampling a 16/44 master to 192/24 is pointless though and won't bring any improvements.
    Problem is HOW does the unsuspecting buyer know WHAT type of recording they are listen to ?

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    1. Good point about the DR database:
      http://www.dr.loudness-war.info

      Good place to visit for information on the various releases!

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  4. Great blog. I appreciate your measurements, your opinions and your open mindedness. I cannot say that I disagree. I happen to be a Mch classical music guy, and so most of what I listen to happens also to be in hi rez, to which I include 48k/24 bit Blu-rays.

    I am an agnostic about whether a well made hi rez recording sounds better than an equivalent CD. We can listen to SACD's in stereo from the DSD or the CD layers. I do not listen that way much, and I am not sure I can hear a difference. Others I know hate you because they think you dead wrong on this.

    Since I believe we are lucky if we can even hear up to 20K, I believe it possible that two things might make a difference, bit depth and filter artifacts coming into the audible band. Since I doubt that good CD's are going to overflow the available 16-bits, the maximum dynamic headroom should be no different for high rez and CD. Therefore, bit depth could only make a possible difference at low levels, below what a properly dithered CD can do. Is it audible? Perhaps very subtly under ideal listening conditions, but we are talking about potential differences these days probably below the -100 dB area.

    There may be a bit more to the filter artifact idea. Filter induced pre-ringing is the latest bad boy, both on the recording a-d and the playback d-a sides. Hi rez minimizes this by shifting it way up in the ultrasonic range, but with CD, it might trickle down into audibility. Meridian has tackled this problem, if indeed it is one, via apodizing filters in their top cd player that turns pre- into post- ringing, where it will be masked by the actual musical signal. I also know that we can clearly see preringing on scope photos of high frequency pulses at 44K sampling. I have not heard the Meridian player, and I am doubting that this is gee-whiz audible. But, I am wondering if there might be a little bit of a sonic edge (pun intended) to doing this.

    I do have a San Francisco Symphony Blu-ray SFS at 100 which has been upsampled from the recorded 48K to 96 and apodized on the disk via Meridian. It sounds really good, but so do some other SFS Blu-rays at straight 48K. Others are not as good, but we are back to the engineering of the recording thing, which I agree with you, makes a big difference.

    As a footnote, the world only recently became aware that Audyssey EQ in all prepros and AVR's was downrezzing everything internally to 44-48K. Actually the processors were, not Audyssey itself. It did its thing and sounded great, nonetheless. But, who knew? So, it turns out I have been listening at less than Hi rez sampling rates all along. And, unless I am willing to turn Audyssey off, which does not sound as good, I just will not be able to hear the magic of Hi rez sampling. I will say that pure DSD, which my prepro can do, just does not sound as good as PCM-converted, downrezzed to 44K, Audyssey EQ'd music. I have not had the heart to tell a good friend about this. He loves Audyssey, but he also swears he hears a big difference between the DSD and CD layer on SACD's. But, possibly there might still be one due to the elimination of a-d preringing on the DSD recording.

    Or, is the preringing thing so miniscule as to be inaudible?

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    1. Thanks for the note Carl.

      About 7 years ago, when my son started crawling around and sticking his fingers into everything, I was forced to move my system downstairs - rendering my 4.1 system down to 2.1. I do miss multichannel. Hopefully next year I'll get a bigger house and really get the home theater room going. I already have all my surround SACD, DVD-A, and Blu-Rays in multichannel FLACs ready to rock through the computer system :-).

      Yeah... All the buzz with digital filters and pre-ringing these days... I'm not sure about that either as I posted before:
      http://archimago.blogspot.ca/2013/06/measurements-digital-filters-and.html

      Using higher sample rate will push the ringing further into the ultrasonic range so that's a good thing assuming there's potential for audibility. I have my doubts with real music though and don't know if there are studies demonstrating this effect as being audible enough to pass controlled testing. (Love to see any links or references if anyone has 'em.)

      Interesting about the Audyssey EQ downsampling to 44-48k. Wondering if there are any computer-based software solutions that can calculate multichannel DRC at 24/96 as a flexible solution... Will definitely be something I'll be looking into next year once I get a proper room set up.

      You also hit another sore point about DSD/SACD - no native digital room correction due to limited DSP processing options (sure, DSD --> PCM is an option but takes away from the DSD mystique). I agree with you that digital room correction is important and makes a very audible improvement.

      "Others I know hate you because they think you dead wrong on this." - Ah well, haters will hate but as per the links, I'm not the only one talking like this. In fact, I think I'm not even that "hard-core" objectivist since I admit to liking/wanting 24/96 :-).

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  5. Archimago, another excellent post as usual :-)

    re: Wondering if there are any computer-based software solutions that can calculate multichannel DRC at 24/96 as a flexible solution...

    Have a look at Acourate, which can do multichannel DRC. I wrote up on it here, but did not have a multichannel set up. However, several folks on the Acourate forum have... Btw, Acourate uses pre-ringing compensation and is an interesting read.

    Cheers!

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    1. Nice! Thanks Mitch... Will give it a try when I get MCh up and running.

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  6. Thanks for the blog firstly - have just come across it and there's a lot of interesting tests and your musings too.

    With regard to high rez, have you read the article by Michael Vest from Digital Audio Denmark about advantages of DXD (24bit/352.8khz) for the the initial A/D process? Whilst it's discussing the advantages of A/D conversion in very high rez PCM over DSD , it possibly touches on some very good points which can apply to a discussion about different PCM formats.

    Here's my own summary: it talks about the far better impulse response of A/D at the high resolutions with DSD touted as being practically perfect, DXD being incredibly close. Secondly, it discusses being able to use filters which are of a much shallower slope than Nyquist dictates whilst that error not effecting the audio band - therefore all ringing can be greatly reduced. In other words, recording at 352.8KHz means that you can have all the possible frequency range benefits of 88.2 but with a more perfect impulse response and almost zero risk of ringing effecting anything in that 88.2KHz sample-rate window.

    Now, this is all in the A/D process yet audiophiles only seem concerned with the D/A process, kind of forgetting that the format they are given has most likely been chosen to get the best A/D conversion accuracy they can and D/A not considered as that aspect is out of the studio's hands!

    Decisions on what format it comes out on is nothing to do with the recording studio nor how the consumer decides to play it back (with downsampling, upsampling etc etc). So in a sense, the argument about whether anything above 24/96 is worthwhile for playback is kind of just audiophiles arguing amongst themselves whilst the people on the recording side ignore them and do what's best for their sonic needs..

    Have a read of it if you haven't seen it before: http://www.merging.com/uploads/assets//Merging_pdfs/dxd_Resolution_v3.5.pdf

    I'd be interested in what you think too.

    Personally, as someone setting up a home studio, I think that recording at very high PCM resolution is neither here nor there - it's only down to convertor cost and storage space and with that convertor cost also comes great functionality, connectability and great sound at the lower resolutions, so I may as well... People can then replay at whatever rez they fancy! As DACs with high sample rates become more readily available, it causes no harm in receiving the high rez format and making one's own decision on how best to play it back for best sonics. It would seem daft to restrict choice from a position of belief or ideology.

    Cheers.

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  7. Hello. I just found your Blog as of Yesterday and I also left comments on your review of your Sony LD player - which I so enjoyed. BTW - I believe your Blog is Fantastic ! It's interesting you brought this subject up. While I've done many A/B listening test between CD/MP3 ( although TRUTH be told @256K not 330kps) with what I "challenged" recordings ( aka. CCR albums for example - obviously the gear was not as well miked as today's isolated multi- mic procedures ( even in a 2 ch final mix they might use 8 mics when recording a drum kit ). And while I'll agree with your results - and I total agree with the whole loudness War BS destroying the dynamic range on today's "remastered" discs.I remember way back in the day when I read articles about when studios were 1st transferring their Master Tapes to CD for the 1st time, and I remember how in one interview with Martha Fine she said that she believed that there wasn't enough resolution ( nor Space !) in the format to get the entire analog wave form off the tape w/out some type of error like you did not have with vinyl and that's why the record would sound better I've A/B my records VS it's CD counterpart. While I know IF you spend enough money on a turntable, stylist, etc etc etc - "they" say the vinyl sound better - but my little 1980 $300(USD) Technics SL-7 will have to do - and the CD sounds fine to me. OH- BTW - I 2 owned Paradigm Speakers - the Export Monitors - and I flat out loved them. However - since @ heart I'm really a Movie Guy ( I was an IA certified 35mm Film Projectionist who worked in several THX Certified Houses) I'm really more concerned about the compressed sound formats on the DVD vs their Blu-ray , and YES- even Laserdisc ( because of their 2 ch. LPCM soundtracks )counterparts. Here's the link to my Blog: Hope YOU enjoy. http://2x-file.blogspot.com/2012/04/dirty-little-sound-secrets-about.html

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