…than most of the DVDs – and few BDs, as I read also in some forums. I don’t want to talk about MUSE laserdisc audio now, because I’m not expert in that branch, but whoever wants to talk about it, is welcome!
OK, let’s start!
NTSC laserdiscs could contain a different combination of soundtracks:
- two mono analog
- one stereo analog
- two mono analog + two mono PCM
- two mono analog + one stereo PCM
- one stereo analog + two mono PCM
- one stereo analog + one stereo PCM
- AC3 + one mono analog + one stereo PCM
- DTS + one stereo analog
I’m pretty sure there is no AC3 laserdisc with two mono digital soundtracks, as PCM is used for stereo (surround) soundtrack, and there are almost no DTS laserdisc with two mono analog soundtracks (Mortal Kombat is an exception), as analog is used for stereo (surround) soundtrack, but I’m sure there are NO laserdiscs that contain both DTS and AC3 soundtracks!
Things are easier for PAL laserdiscs:
- two mono analog (on laservision)
- one stereo analog (on laservision)
- two mono digital
- one stereo digital
- DTS (well, only one title ever released!)
The PAL laservision is practically another standard, as PAL laserdisc video could be watched on old laservision player, but digital soundtracks could not be heard! The contrary is usually not true, as the most part of the PAL laserdisc players could also play analog soundtracks. There are NO AC3 PAL laserdiscs!
Now, let’s take a closer look at the different soundtrack types:
Albeit analog soundtrack on laserdisc is the worst of the possible ones that could be found on it, the quality is pretty good – here you are some numbers:
- Frequency response: 20-20000hz (±3dB)
- Signal-to-noise ratio (CX off): >50dB (up to 58dB)
- Signal-to-noise ratio (CX on): >62dB (up to 74dB)
- Channel separation: >50dB
Not that bad, uh? Better than vynil, audio cassette, second only to VHS HiFi Stereo. It could contains also surround sound; some concerts could be found only on analog laserdiscs, as they are never released with digital audio; the most part of japanese bilingual laserdiscs have the japanese language recorded onto the analog soundtrack… why? Maybe because it sounds better? The answer is yours…
PCM (Pulse Code Modulation)
The first (and most used) digital soundtrack that appeared on the laserdisc format was PCM, stereo or dual mono, 16bit 44.1KHz 1441kbps – it has the same technical specifications and quality of the CD-audio.
- Frequency response: 4-20000hz (±0.1dB)
- Signal-to-noise ratio: 96dB – up to 117db (EIAJ)
- Dynamic range: 96dB – up to 99dB (EIAJ)
- Channel separation: 80dB – up to 90dB (EIAJ)
- Wow & Flutter: <0.001% (EIAJ)
All the PAL laserdiscs after the end of 1980s have digital audio; NTSC continued to have both analog and digital soundtracks, as the standard allowed it; several surround types could be found on laserdisc, not only the famous Dolby Surround, but also DTS Surround, UltraStereo, CHACE surround.
AC3 (Dolby Digital)
The first AC3 laserdisc was “Clear and Present Danger” and was released in 1995; the AC3 soundtrack is stored in the right analog channel, and is RF modulated; to be decoded, a laserdisc player with the AC3 RF output is needed, and must be connected to an RF demodulator and a Dolby Digital decoder, or to an amplifier with built-in RF demodulator and DD decoder.
The AC3 soundtrack has always the 384kbps bitrate at 48KHz, almost always 20bit 5.1 channels, but in some (rare) cases the number of channels could vary – usually during extra material like making of, documentary etc.
I found no proof (until now), but there are clues that the theatrical mixes are used for AC3 laserdisc soundtracks “as is”; in fact, many argue that laserdisc Dolby Digital sounds better than the DVD counterpart, also if the latter has an higher bitrate; indeed, most DVD DD soundtracks are mixed taking in account home users, and they should sound good with any kind of audio configuration, and hence it’s a sort of compromise – that’s why, to avoid this, some titles offered both multichannel and stereo Dolby Surround encoded tracks. At the contrary of DVD that almost always use near field mix, laserdisc usually use the same DTS theatrical far field mix, and has that “in your face” sound typical of theaters.
Someone could think that is not possible, as the theatrical AC3 soundtrack is 320kbps, while laserdisc has 384kbps… think that the LD AC3 is stored on analog form, and surely the signal contains some sort of stronger error correction, due to the fact that analog reading is not perfect; also, it is possible that the signal is simply padded from 320kbps to 384kbps, as it was more economic to take the theatrical mix and copy to laserdisc than remake a home version…
DTS (Digital Theater System)
The first DTS laserdisc was “Jurassic Park” and was released in 1997; DTS soundtrack takes the place of the PCM soundtrack, leaving free two analog tracks, (almost) always used for the movie soundtrack, allowing the owner of an old analog-only player, or who has not a DTS decoder, to listen to it. To be decoded, a laserdisc player with digital output is needed, and a DTS decoder, or an amplifier with built-in DTS decoder.
As the DTS soundtrack is in place of the PCM one, it has the same technical data, 16bit 44.1KHz 1441kbps but, at the contrary of the PCM two channels, it has 5.1 discrete channels.
The laserdisc DTS soundtrack IS NOT the same of the theatrical one: in fact, in theaters, DTS uses a different codec, APT-X, encoded as ADPCM at 882kbps and recorded on CD-ROMs, with a compression of 4:1, while DTS on laserdisc uses Coherent Acoustics perceptual coding compression scheme, encoded at 44.1KHz with a bitrate of 1235kbps (incapsulated at 14bit 44.1KHz, padded to 16bit, to lower the white noise, when playing the track without a decoder, by 12dB) and a compression of 3:1. Hence, the DTS laserdiscs should be better than the theatrical DTS, as the home codec is newer and better, and bitrate higher with less compression.
As almost all DTS DVD have the so-called “half bitrate” soundtracks (754kbps padded to 768kbps) instead of full bitrate (1509kbps padded to 1536kbps), the laserdisc DTS soundtracks is always better than “half bitrate” DTS DVD; in some cases, could be preferable to full-bitrate DTS DVD due to different mixes used.
[added on 2016/11/03]According to many posts written by Disclord (R.I.P.) on LDDB forum, very often the DTS LD used a 18 bit masters (and sometimes 20 bit), while the AC3 LD often used 16 bit masters (but 18 bit too; dunno about 20 bit, though); also, surround channels on the first year or two after the introduction of DTS laserdiscs are mixed +3dB louder.[end]
Using a laserdisc soundtrack for preservation purposes is often a good choice; when the DVD or BD soundtracks are of low quality, or technically inferior, or “improved”; when the DVD or BD soundtracks have different formats; when the DVD or BD have no soundtrack in a certain language; or, simply, when there are no DVD or BD of a certain title or version at all!
There is only a price to pay: capturing and converting laserdisc soundtracks is an HARD task… but really rewarding! – just finished JP2 AC3 and DTS, I know what I’m talking about… (^^,)
Quote:This paper presented listeners with a choice between high-rate DVD-A/SACD content, chosen by high-definition audio advocates to show off high-def’s superiority, and that same content resampled on the spot down to 16-bit / 44.1kHz Compact Disc rate. The listeners were challenged to identify any difference whatsoever between the two using an ABX methodology. BAS conducted the test using high-end professional equipment in noise-isolated studio listening environments with both amateur and trained professional listeners.
In 554 trials, listeners chose correctly 49.8% of the time. In other words, they were guessing. Not one listener throughout the entire test was able to identify which was 16/44.1 and which was high rate , and the 16-bit signal wasn’t even dithered!
That’s why we all love so much laserdisc PCM soundtracks…
I think this info could be useful:
disclord Wrote:NEVER listen to a non-encoded disc with CX on – its not been properly encoded for the CX noise reduction and will not sound right. It’s not there to be used on non-CX’d discs. However, an analog CX disc can be listened to without CX decoding – that was one of the design goals, that it not sound noticably weird when not decoded – it will just have more background/disc noise. Every digital title that has the analog soundtrack duplicating the digital has CX – discs with commentary/bilingual/AC-3 discs do not have CX (some are improperly auto encoded with it though, sadly). DTS discs with analog stereo tracks are all CX. CX requires that the two encoded channels be related, i.e. stereo or mono, to decode correctly, thus incorrectly encoded commentary/bilingual are not in CX compliance.
(found here: http://forum.lddb.com/viewtopic.php?f=12&t=1148)