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 Post subject: CX encoding
PostPosted: 30 Apr 2012, 20:10 
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I've read up on CX encoding and understand the process, but has anyone really ever studied its effects? I'm going to give it a whirl with some of my analog only discs on and off.
And was this ever applied to the digital tracks as well?
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 Post subject: Re: CX encoding
PostPosted: 30 Apr 2012, 20:28 
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sdraper wrote:
I've read up on CX encoding and understand the process, but has anyone really ever studied its effects? I'm going to give it a whirl with some of my analog only discs on and off.
And was this ever applied to the digital tracks as well?

CX was never implemented on digital tracks because it was designed specifically for analog audio on LDs. I suppose it kind of akin to Dolby Noise Reduction--something that was specifically made for analog.

Hence, it's not really needed for digital audio.
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 Post subject: Re: CX encoding
PostPosted: 30 Apr 2012, 21:03 
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i have discs with and without the CX, also noticed that some CED discs have CX
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 Post subject: Re: CX encoding
PostPosted: 30 Apr 2012, 21:43 
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Its original application was to LPs. Unlike the competing dbx, it was designed to give acceptable results when the decoder was not engaged, but like dbx, Dolby A/B/C, &c, it should not be used on Red Book digital audio. (Some people swear by the results of using these schemes with the old 12-bit nonlinear PCM adapters for recording audio on Beta or VHS tape.)
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 Post subject: Re: CX encoding
PostPosted: 28 May 2012, 00:03 
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Having studied noise reduction and digital audio over the last I can't remember how many years, I'm just going to throw some information out there rather than address information indvidually.

Noise reduction was developed as a method of removing tape hiss/noise from magnetic media. Due to the arrangement of particles, and the way tape works, there's an inherent hiss that you couldn't get around then. Variations on tape forumlas lead to tape that was less prone to noise; but back in the early days, the ferric oxide forumation could lead to excessive noise. The smaller the track, the more noise.

To get the record straight, noise reduction systems were not designed to be played without a proper decoder; Dolby B was a form of modified Dolby A that allowed more acceptable results without the decoder. Dolby B worked on only the upper half of the spectrum, it's compression is not as noticeable in that region; so decoderless playback was accepted. and a common practice. I've never heard a Dolby A recording to say how it sounds decoded, but it was only ever really used in professional studios and, for a brief time, optical soundtracks. Dolby C was basically a double B; it doesn't sound well decoded. I've never heard Dolby S; as I don't have any tape decks that feature it. However, I've been told that it was designed to be "backwards-compatible" with Dolby B. A B decoder won't fully decode an S recording, but some benefit would be realized. Part of the reason Dolby B was used on practically every commercial cassette was it's compatibility with no decoder; but it's also ironic the idea of mass-producing recordings with Dolby B rarely ever worked. Most mass-produced tapes were quickly dubbed on cheap tape, leading to an inherent loss of HF information Dolby needs. There was also a problem with calibration; if your decoder wasn't calibrated to what your tape was recorded with, it didn't sound right. The problem was worse with Dolby C, however only higher-end home decks featured C; I've never seen a portable or car unit that did it (I also haven't looked).

CX was designed originally for vinyl records, vs dolby's intent on using it for tape. It wasn't ever designed to be played back without a decoder; it's just many people found it acceptable. I've got a couple of Laserdiscs that aren't CX encoded; and I haven't captured audio samples of CX encoded examples with and without decoding on. So I can't really comment on how it worked. It follows the typical compansion formula that all noise-reduction system uses, I don't know ratios or thresholds. Come to think of it, I don't even know how Dolby compresses it's audio since the papers mention a lot about sliding band.

dbx was the oddball that did the best job. I picked up a model 122 NR unit last week and have been giving it a lot of testing. It's recordings sound very ugly without decoding. While it's using the same compansion technique, dbx applies a much higher ration (2:1) across the entire spectrum, and it also applies an EQ curve similar to what's used for RIAA on LP's. This reason for applying the curve was simple...take advantage of how the tape actually stores audio. By reducing the bass and boosting all the treble, you're basically kind of brute-forcing normally lost high frequencies. Tape pre-amps already do it, there's various curves in the RTR days and I believe one standard one for the compact cassette; but dbx just applies additonal preemephsis. A form of dbx was used in the MTS stereo standard as well.

Dolby simply set out to reduce noise; cx and dbx both set out to actually enhance the dynamic range a bit, dbx more so than the others. Dolby *did* get in to the expansion of dynamic range a bit with a system called HX, Headroom eXpansion. This was modified by B&O and marketed on the consumer market as HX Pro. HX Pro was not a noise-reduction scheme, nor did it require a decoder. It worked by modifying the amount of bias applied to the tape based on the amplitude and phase of the high frequency. If you over-bias a tape, you start to lose the HF response. Since HF signals tended to self-bias already, the additional bias level from the tape would cause it to actually be reduced; this was one of the reasons cassettes usually had such poor response. HX Pro modified the level of bias put on the tape, according to what the HF content being recorded was. This kept the amount of bias on the tape more even and allowed the self-biasing high frequency noises to remain.

The effects of any compansion system depends on how calibrated they are. Overall, it's what I call a neat trick; dbx was a mind blower. It's still not perfect, and at times, you can tell where the dynamic level is a tad off. CX seems to work very well on LaserDisc, I've not once switched it off due to excessive pumping.

But, ok, these systems and digital audio. Digital audio, by it's nature, usually doesn't need noise reduction. It's a digital stream afterall, isn't it? Well, there are a *few* cases where a noise-reduction compasion process will benefit.

A prime example is the non-linear 12-bit format. 12-bit sounds pretty good and all that, but it's still not a lot of dynamic range, you'll get quantization noise if you try to express something with more dynamic range. It's amplified by the fact if you're using non-linear. The compression and expansion of something like CX or dbx lets you get around that.

Believe it or not, compansion techniques WERE in fact developed for digital. The HDCD format is compansion.
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 Post subject: Re: CX encoding
PostPosted: 18 Sep 2012, 03:57 
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Is there a way to definitively determine if a LD analog track is CX encoded? I know the jacket should indicate it, but is there some way to test if the jacket is accurate?

My players (Pioneer CLD-D703 and Panasonic LX-900) don't seem to give an indication of CX being present, nor any sort of CX on/off button.


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 Post subject: Re: CX encoding
PostPosted: 18 Sep 2012, 14:38 
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Tha DA/CX button on the 900's remote will switch the CX on and off if it doesn't have the auto CX coding, and most discs do. The onscreen display will show CX ON/Off. It's the same for your pioneer, the DA button will switch it on and off, again, only if it doesn't have auto switching. If you play an old Non CX disc with CX on, you will get audio level changes constantly as the CX tries to decode audio that wasnt encoded. Once minutes/seconds were added to discs, so was auto CX switching. It can't be over ridden on anything but the early top loading players. The instructions on how to activate CX are in the manuals.
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 Post subject: Re: CX encoding
PostPosted: 19 Sep 2012, 02:57 
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Thanks for the guidance, discord. I played around with some of my oldest discs and found, just as you stated, that the remote button does turn it on/off. I'm guessing it is best to listen to non-encoded discs with it set to off, though I haven't cranked up the volume to really test out that theory.

So, if I'm understanding this correctly, practically every LD produced after 1987 or so, has the CX encoding on the analog track(s). This would imply that there are thousands of LD jackets that should/could carry the CX emblem but do not. I supposed that once digital tracks became the norm, the CX emblem became less and less important over time.
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 Post subject: Re: CX encoding
PostPosted: 13 Dec 2012, 05:55 
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Some of the older discs you still have to manually put the CX on. I was watching my Japan 1981 Ventures.

The Ventures: Live in L.A. [MP018-22MP]

Both the jacket and disc labels have the CX encoded logo, but the disc is not coded to automatically put the CX on so you have to do it manually. I know I have a couple other discs that are the same.
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 Post subject: Re: CX encoding
PostPosted: 14 Dec 2012, 03:05 
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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.
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 Post subject: Re: CX encoding
PostPosted: 14 Dec 2012, 04:56 
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Well according to my disc label it has CX on it (and also on the jacket) but none of my players automatically activate the CX when I play it, which is why I have to activate it manually. So I'm guessing the LD is just not coded to put the CX on.


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 Post subject: Re: CX encoding
PostPosted: 14 Dec 2012, 05:38 
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i didn't know that you could turn on CX if the disc didn't have it.
or that's how the 3 players i've ever used worked.
3070, r7g, 503.
i could never turn on something that wasn't there on the disc.
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 Post subject: Re: CX encoding
PostPosted: 14 Dec 2012, 05:42 
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Right, early discs and players didn't have auto CX activation. That was added when extended code was added to the LaserDisc format - when we got minutes/seconds on CLV, CAA encoding, etc.... Around 1984 or so, but not every disc used auto CX on. If the disc says its CX, it is, and you might have to activate it manually if it's an old analog only title. ALL digital sound titles, even the very last two Paramount US titles, have auto CX for the analog tracks and some discs without CX have auto OFF so it can't be turned on with a player that looks for the CX coding. That was to prevent consumers from using CX with discs that were not CX encoded.
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 Post subject: Re: CX encoding
PostPosted: 14 Dec 2012, 05:44 
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rein-o wrote:
i didn't know that you could turn on CX if the disc didn't have it.
or that's how the 3 players i've ever used worked.
3070, r7g, 503.
i could never turn on something that wasn't there on the disc.


Early discs, from 81 to 83 or so didn't have auto coding so you could turn CX on and off. And the first few Pioneer players with CX built in, like the LD-1100, had to have CX activated or deactivated manually, so you had to look for the CX logo on the jacket or disc label.

On your late model players CX can, but shouldnt be turned on on all early discs, like DiscoVision and the first few years of Pioneer, unless CX is indicated on the jacket or label, like Olivia Physical. Grease always showed as being CX encoded in Pioneers catalogs, but they never pressed it with CX encoding, so the jackets never had the logo.
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 Post subject: Re: CX encoding
PostPosted: 14 Dec 2012, 06:04 
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disclord wrote:

Early discs, from 81 to 83 or so didn't have auto coding so you could turn CX on and off. And the first few Pioneer players with CX built in, like the LD-1100, had to have CX activated or deactivated manually, so you had to look for the CX logo on the jacket or disc label.

On your late model players CX can, but shouldnt be turned on on all early discs, like DiscoVision and the first few years of Pioneer, unless CX is indicated on the jacket or label, like Olivia Physical. Grease always showed as being CX encoded in Pioneers catalogs, but they never pressed it with CX encoding, so the jackets never had the logo.


:think: on early discs, if there is no CX i can't turn anything CX on with my 2 players i have now.
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 Post subject: Re: CX encoding
PostPosted: 14 Dec 2012, 06:13 
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update: i just checked both of my players now, if the disc has or doesn't have CX i can't turn it on, and it doesn't
say if it's on or off. so what is that about?
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 Post subject: Re: CX encoding
PostPosted: 14 Dec 2012, 06:24 
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rein-o wrote:
update: i just checked both of my players now, if the disc has or doesn't have CX i can't turn it on, and it doesn't
say if it's on or off. so what is that about?


Pioneer's stupid feature decisions... The DVL-700 is kinda the same - there is no indication of CX on or off with auto coded discs and with early CX discs without auto switching code, you have to manually switch through L/R-Stereo-L/R-Stereo to manually turn it on with old discs and listen for a drop in background disc noise to make sure it's on. The instruction manual gives NO indication that this can even be done - it speaks only of auto CX, even though there is no CX indication that it's on. My EAD and Panny 900 both show CX on or off on-screen and my CDV-488 and CLD-1010 both have displays on the player for CX ON.
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 Post subject: Re: CX encoding
PostPosted: 14 Dec 2012, 06:28 
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O.K. i'll try again tomorrow, too late now for me.
i thought i used to see the CX after going through the L1 R2 etc.
but i checked 3 discs and didn't see it, i'll try on an analog only disc tomorrow to see what it does.
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 Post subject: Re: CX encoding
PostPosted: 14 Dec 2012, 06:39 
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rein-o wrote:
O.K. i'll try again tomorrow, too late now for me.
i thought i used to see the CX after going through the L1 R2 etc.
but i checked 3 discs and didn't see it, i'll try on an analog only disc tomorrow to see what it does.


It will NEVER be a manual ON with digital LaserDisc'a. Digital discs have auto CX. You have to turn on CX manually ONLY on early analog-only titles, and the vast majority were not CX encoded. It was mostly Pioneer Artists analog titles (although their first two, Liza and Paul Simon, didn't have CX) and music titles from other studios. Analog mono titles rarely got CX encoding. It was hit or miss until digital sound came along, and even then, digital sound was not always used. All discs having digital sound with CX on the analog tracks didn't happen until the late 80's and early 90's. Before that, no digital, no CX, was the norm. Automatic disc coding to tell the player the disc was CX encoded started in 1983 or so but no player used the auto code until the LD-700 in mid 84.
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 Post subject: Re: CX encoding
PostPosted: 16 Dec 2012, 08:16 
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disclord wrote:
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.

Thanks so much for posting this info. I feel like a light-bulb just turned on over my head. :idea: I kinda suspected that CX requires the use of two related channels but never knew it it to be true. Now I understand why a boxed set I own contains some discs with the CX logo and some discs without it. Turns out that the discs with the CX logo have a single language mono track (on both the right and left analog tracks), and discs without the CX logo have analog bilingual tracks (e.g. left track English, right track Japanese). It all makes sense now. CX needs to occupy both left and right tracks, and the two tracks need to be a mono or stereo version of the same recording.

...which also explains why Brute Force (1947) [RGL9506] has a commentary track and is CX encoded. It all works out because Roan put the commentary on both analog tracks.

Did everybody else understand this all along? Am I the only one this late to the CX party? :oops:
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