Saturday, April 14, 2012

Dirty Little Secrets- "Surround Sound" formats on LVD , DVD, & BluRay

Generally speaking - the LPCM tracks on a CD sound better than a MP3 recording of that same source material.. Now - the Original Final Master Tape/Disc recording has more to do with the way something sounds overall more than the recording format, I know that. However the higher bit rate produced by the CD Red Book standard of 1411kbps for 2Ch stereo does help produces better dynamic's. So how do the compressed sound formats on DVD compare? Well -here's the thing about AC3RF. The bit rate on Laserdiscs is recorded at 384 kbps, 5.1 Ch. or in other words (pun intended) a mere 64kbps per channel, which is sadly enough about ='s the lower 2CH MP3 128 kbps rate, which just so happens to be the "streaming" bit rate utilized by many music server's, for copyright law purposes.    
       Now, it's generally known that in order to get "good" sound playback from MP3, don't download or record in ANY bit rate less than 256 kbps.(My person 2cents on this subject here after many blind A/B listening test is that vocals hold up well, but I can still here difference in some things between the LPCM version and MP3, like the hi hats, and other cymbals used in a typical drum kit, for example) MP3' streams at the bit rate of 64kbps very often have a "metal" echo like sound , like many stations (channel numbers) on the Digital Sirius XM Sat/Internet Radio network.

Ok, with all that in mind, add to that fact that Dolby Digital 5.1 just doesn't have the same dynamic range as LPCM and to make matter's even worse (hold on to your hats1) DDAC3 on many DVD soundtracks is not always 5.1. (the case with many movies produced before 1991 that have not been "remastered") and many disc do not advertize this little Dirty Fact. Some do, but in many cases, it's kept a secret.
CRYSTAL chip used for most surround EX receivers before HD.
          A DD track can be, and is often only 2.0 or 2.1 , 3, 4, 4.1, 5.0 or even worse, I have the Original (late 70's) Battlestar Galactica Movie in which the soundtrack was only produced in......that's right...MONO. So this disc is only DD 1.1 ! and therefore, only the Center, and LFE CH's "light" on my surround receiver's optical Ch Indicator display. So, what about the bit rates of these disc? Is the total bit rate (up to 440kbps on DVD) utilized for those disc that contain less than 5.1 ch.'s in order to help maintain fidelity? since they are "missing" Channels worth of info.? Many times that's not the case. The BSG disc is only recorded at 128kbps (64kbps per Ch). If your 2.0 DD AC3 (128kbps) encoded disc is put through your surround's Pro-logic II processor, then you have only 128kbps "worth" of digital info for all 5.1 Ch.'s. You do the math. That's why (my 2cents here) DDAC3 often "sounds" worse than the LD's Digital  LPCM soundtrack,  ( even though that track is only 2-ch, and not 5.1 ) and by far, in my opinion, worse than the DTS track (750kbps DVD, 1500kbps LD) soundtracks. The DTS track LaserDisc are nothing short of amazing !

With the BluRay Disc, the HD soundtracks, on most titles are being presented, or so it sure seems,( regardless of the fact that they can deliver constant ,not variable, bit rates up to 6.0 Mbit/s) at the 1500kbps "core" rate for DTS, (which still sounds Great!) in order to maintain / and remain "BACKWARD COMPATIBLE" (compliance for more widespread acceptance) with older gear that does not have HDMI connections or HD surround decoding, since the older Crystal chips can handle this data bitrate through the optical input.

          BOTH DDTHD & DTS-HD require an HDMI cord to send those higher multi channel bitrates to an HD capable surround decoding receiver because the standard coax or optical digital out not only won't do it (this may be to stop anyone from making a direct digital copies of the HD 7.1 surround track) but, my older 2002 surround receiver's DD/DTS chipset, can only process a maxium of 1.5Mbps anyway. If "they" sent a 5 or 7 ch HD track "out" to my surround processor from the Blu-ray player, with a higher data rate that is currently only supported by HDMI) the surround processor on board an non HD surround receiver would not be capable of processing it. Now, both TrueHD and DTS-HD use lossless data compression to save space on the disc. The LPCM is fed into the encoder and compressed to save space.

         "They" realize that most customers will never know the difference, or could tell the difference, or own the level of equipment that is needed to tell/hear these differences anyway, and or, are just to stupid to even bother taking the time to research these details, which I believe has been more than proven by the number of El-cheapo piece of crap "Home Theater in the Box" and "Soundbars" (with 5.1 "down converters built in" to them) that are for sale out there(or have sold) already. The only way I could listen to the 6 track LPCM surround MasterTrack (the exact copy of the studio Master)or the Dolby or DTS HD track was because my HDDVD player had 6 ch. analog outputs, and my receiver had 6 ch analog inputs for "SACD/DVD-A" players. I will say the HD tracks hold up well very well when compared to the LPCM Master, and that's because on playback, the lossless codecs use whatever bandwidth they need at any given moment. 

             PCM bitrates are fixed, even when there's very little sound being played. I will say this. The "sound" of the "rain" on the 7.1 LPCM track of "The Crimson Tide" on Blu-ray was more "spot on" than any other "rain" track I've had the pleasure of listening to. While the Standard DD track did a damn good job considering the compression that was being used, nothing, and mean nothing, comes as close to the real life sound of rain than this. WOW!