HDCD: an investigation

Don't get me wrong, it STILL decodes HDCD! Only now, you have no way to know for sure (except for the improvement of the sound, if any) if your disc is HDCD

 

I recently got myself an oppo 981hd, and have been surprised that several of my cds are hdcd encoded:

Various Artists - For the Masses (depeche mode tribute album with fantastic sq)
Beach Boys - Pet sounds (european 2000 mono)
Beck - Sea Change
King Crimson - In the Court..

I'll probably find a few more aswell. It's a bit annoying though that the oppo only displays hdcd on the video monitor for a few seconds after inserting a disc, because I don't like to have my tv on while playing music...

 

I understand. Still, I like seeing the little HDCD light on.

 

There's lists of HDCD here and here

http://www.head-fi.org/forums/showthread.php?t=67082

http://www.hifimusic.se/hdcd/index.php?p=home&lang=en

 

You mentioned wanting to do that to the undecoded file...that's what I don't understand. What would you hope to achieve?

 

I had the same problem playing them in older versions of foobar, but kept the files around for archival purposes (since the command-line FLAC decoder could still read them). Try version 0.9.4.4 (the latest as of writing this, which I just installed -- if you aren't using it already, that is) and see if it makes any difference. I noticed most of my 24-bit (or maybe 20-bit pretending to be 24-bit) full-album FLAC files will play now, provided I remove any embedded cuesheets first (they still work with external .cue files, which is nice).

 

Sorry, I meant taking the decoded 24 bit file (when containing more than 17 bits) and bringing it back down to 16 bit.

 

Did you use hdcd.exe or the WV plugin to capture the HDCD data? Because I use the latter, and I cannot get foobar 2k 0.9.4.4 to play flac files created with flac 1.2.0 (the latest version). (Nor could I get it to play flac 1.1.4 files)
F2K properties says the files are 20-bit, and when I try to play them this is the foobar error message:

Decoding failure at 0:00.000 (Unsupported format or corrupted file):

followed by the filename.

None of my flacs have embedded cuesheets.

 

Turns out it must be hdcd.exe vs the plugin, because the same track 'ripped' with hdcd.exe , then converted to flac, can play in foobar2k. F2K 'sees' the hdcd.exe flac file as 24-bit (in its properties display), whereas it 'sees' the WAV plugin flac as 20-bit. (Audition sees both as 20 bit, but I suspect that's based on actual statistics of the data).

I also get different flac.exe messages when compressing the two files...so clearly hdcd.exe and the WAV WMP plugin produce files that are different in some way (though not necessarily an audible way). Which was mentioned/implied already, I think.

 

Yeah, I couldn't play back the files or flac compress them when using the WMP method - I had to open them in Audacity first and then either compress them from there or export them as wav files.

It seems the WMP/Chronotron method outputs "wavex" files rather than "wav" files. Not sure what the difference is but it seems to only be different headers.

Anyway, hdcd.exe ouputs normal 24-bit wav files so I can play them or flac compress them without needing to open them in Audacity first

 

Observation - I tried running a non-hdcd file throught wmp/chronotron and still came up with a 24bit output that was 6db reduced. Does this make sense?

 

Yes, according to the author of the code:

http://forums.slimdevices.com/showpost.php?p=222168&postcount=213

 

I'm not talking about the hdcd.exe prog, I'm talking going through the wmp/chronotron method.

My thinking is that this is a better way to go because I'm assuming wmp's hdcd decoder addresses the filtering options.

 

I used the Chronotron plugin a few months ago. I couldn't remember which files I used the load-then-resave-in-Audition trick on, but it seems it was all of them. (I suspected at the time that it had something to do with wav vs. wavex, but I'm not sure what difference that should make to the FLAC encoder. Perhaps something else embedded in the stream that foobar2000 doesn't like...)

I didn't know about hdcd.exe until I saw it here, although I'm reading the thread on it over at Hydrogenaudio right now. I thought at first that it was hooking into the code in WMP, but it seems the author reverse-engineered the encoding format by hand. (Meaning that if the author releases the source code it should be trivial to port it to Linux or Mac OS or wherever else, as well as incorporate it into various software players.) I'll try it out tonight -- I might have more HDCDs than I think, since the WMP+plugin process is time consuming and I've only been decoding discs that I already knew were HDCD-encoded...

 

Yes. It's because you've activated the 24-bit option on WMP.

 

Ah. So it automatically reduced the signal by 6db regardless of how the disc is encoded?

 

I'd already noted some minor differences in the files earlier in the thread -- minute differences in leader silence and length -- but I haven't verified those rigorously. Certainly flac.exe sees them as different -- the WMP plugin causes flac.exe to add a WAVEEXTENSIBLE metatag to the file (= 'wavex"?), while Hdcd.exe causes flac.exe to issue a '24 bit input' warning message.

Yup . Again the only real questions for me remaining is whether the hdcd selectable filters are implemented at playback (or just at encode, as some have claimed), whether low end extensible inforamtion is implemented, and if so, whether the WMP software emulates them. THis will require careful comparison of
undecoded to decoded versions of the same tracks.

 

Apparently. Such behavior, by the way, was mandated by the Pacific Microsonics originally, so that hdcd tracks wouldn't sound quieter than standard tracks. I'm guessing Microsoft retained it.

 

You're right!! I completely forgot about that. I remember the "unofficial" tweaks to undo that for normal cds.

 

Another question- I get a 24 bit output via wmp or hdcd.exe. It appears to be anywhere between 17 and 20 bits depending on signal content. If I add dither (uv22hr), will it properly convert down to 16 bits?

I ask because most files maintain a constant bit reading of 16, 20 or 24, these decoded files are different.

 

Whoops!

I'd certainly like to know if the hdcd.exe code covers all the bases or whether it neglects anything the chip decoders implement.

Not sure how the code could implement any filtering - it chucks out the 24-bit file so quickly it's hard to believe it's done any complex audio processing!

Maybe the benefit I'm hearing really is just from a 6dB attenuation......

 

There is many problem with HDCD and I don't really see any real use for it.

First, one problem is that if you use a CD player without HDCD (like most do), you will hurt the soundquality. You will lose 1 bit of the 16 bit on the CD and the music can be compressed up to 11,5 dB

Secondly, the "good" thing about a HDCD in a HDCD machine is more bits. But do we really need them? Let's calculate:

16 bits CD have 96 db dynamic range.
Your living room have maybe, if you're lucky, 30 dbA noisefloor
The song you are listing to have maybe a crest of 15 db

So 96+30-15 = 111dB. You have to play a average volym of 111 dB to have the CD's noisefloor at the same level as your rooms noisefloor. So whats the use for more bits? And when most people don't have a HDCD ready player, they will get worse sound than the original 16/44.1.

 

Since pcm is linear, for 16 bit input you could also calculate that

Average volume -18dbFS on the source means 13 bits resolution.

Quiet passage 22dB less of the average means 9 bits of resolution, 512 sample values. 8 bits for both positive and negative wave, 256 for each side. And you could count that 1 bit possibly noise, halve the sample counts.

If the average volume is reasonable 80dB SPL, the quiet passage means 58db SPL, normal speech level.

The linear nature wastes 57344 (2^16 - 2^13) samples just for the last 18dB of transients.

 

Well, the hdcd box was a very good ad-converter (still is?), and the hdcd signalling doesn't use all the lsb bits, so it's not like you're loosing one whole bit of resolution.

My hdcd's sound good when played back on regular players, which I think is down to good built in a/d and dithering.

 

Hmm, I just tried a couple tracks from Tool - Lateralus. All it does is lower it 6dB...on the HA thread it said this album has peak extension. The hdcd.exe actually does say HDCD detected, which is interesting.