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Author
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Topic: Setting CP750 Subwoofer Level
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 10-20-2018 11:25 AM
I stumbled onto a peculiarity on the CP750 subwoofer level that I'm amazed I never bumped into before.
When calibrating the CP750 subwoofer output, be sure to be on ANY format other than Non-Sync (preferably Digital 1...which I normally do but didn't on this install).
It would appear that when the Non-Sync format is selected, the 10dB pad used for non DCP formats is inserted on the output, even while in "Alignment Mode." So, if you adjust your subwoofer while the Non-Sync button is selected, your subwoofers will be 10dB too loud!
Just to make sure it wasn't a defective unit, I checked another and sure enough, selecting Non-Sync, even while in alignment mode, drops the subwoofer level 10dB. Mind you, the alignment mode give you the option of setting the "Pro Logic" level for the subwoofer (normally 10dB lower) but this mode was NOT selected.
Current firmware (1.2.8.3) was in use and has been the shipping firmware forever and a day (well since pretty shortly after Surround 7.1 came out).
In fact, this issue is in the release notes for 1.2.8.3 so it is a known "feature" but it has been so long since a new firmware, I hadn't read the release notes in years (typically, just when they come out).
That is all.
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 10-21-2018 02:20 PM
No, not at all. I'm against wasting resources for unrealized gains.
If you have a system that has an effective S/N ratio of 105dB (for example, not necessarily the CP750...which is actually in that ballpark)...and you are putting it into a room that has an NC-30 rating...you have exceeded the limits that can be perceived, at that point. Going for 120dB S/N is wasted because nobody would hear the difference.
You don't know the DSP used in the CP750 nor the D/A and A/D circuits to make the claim that anyone is doing anything better. And EVEN if they were doing something better (as I'm sure they are, the CP750 isn't an esoteric piece, it is the CP50/CP55/CP65 of its day...it is there to play DCinema audio and some typical alternate content.
It has a simple user interface and adequate control interface. In short, it fills a need very well. It is not the best in class in every circumstance but in 95% or more cinemas, it will satisfy their every need, and then some. Again, sort of like the CP50/55/65 and eventually all of the way up to the CP650.
And even in those processor's day, they were not necessarily the best in class. As you, I used a fair amount of Panastereo equipment. I used it primarily for features that the Dolby product didn't have (number of inputs, particularly 6-channel inputs) and for its significantly quieter S/N ratio, particularly in screening rooms. Dolby essentially admitted fault in that department by having a post production version of the CP65 that had "THAT corp" VCAs on the CAT242 instead of the TDA series. I also didn't like the "snaps" that a CP65 made on format changes in those rooms. The CP750 suffers from none of that.
However, there ARE processors out there for the more high-brow systems. The Trinnov Ovation doesn't boast "as good as" a CP750...it boasts "better than the rest." A fair number of people, whom I respect, have really liked it. More power to them. Same thing for the Datasat AP20/AP25 for those that need a processor that does more than the basics and also boasts a better than average audio quality. But Dolby has never been about building the esoteric equipment. They are about putting THEIR technology into a box, and, the case of professional, selling the box with their technology. So, if Dolby were to have some sort of whiz-bang, patented system for tuning a room, I could THEN see them coming out with a new processor for the masses but it would take something like that for it to happen.
But the question remains, with this ever moving industry, will the need for a separate sound processor remain? Dolby has already demonstrated a system that goes straight from IMS to amplifier...done. QSC is going to release their CMS-5000 server in 2019 (if you believe the rumors) and it will go direct to QSYS (their proprietary...sort of...system). There is nobody in the booth anymore turning knobs, pushing buttons or looking at displays...why should there be a box that has those features? For us, when something goes beyond the CP750 capabilities, QSYS seems to be a good answer now that the DCIO-H is available to provide a decent DCinema interface.
QSC's latest traditional processors, the DPMs, reduce the rack height by 1, reduce the user interface (just an LCD screen now) and reduce the button count WAY down because...again, how often are those features being used? And if people need those features, they have those processors too.
It wouldn't surprise me if the JSD100 falls by the wayside before the CP750. The JSD60 is a more clever box (with a semi-major design flaw in having the 2-channel decoder on pair 4 instead of pair 1) that is quite flexible and QSC has other products that satisfies the JSD100 market (DPM, DCP and QSYS). But one thing I've learned about QSC based on dealer meetings...if you buy it, they'll make it. They'd rather not discontinue products that sell.
For the screening room and complex room market, I think QSYS is the platform...it is as complex or as easy as the designer wants/needs it to be. But that isn't Dolby. Dolby's boxes has typically been the vessel to sell their technology (Dolby NR cards were in every CP that they made for film). The CP750 is an oddity in that it doesn't carry any real proprietary technology in it. Without it though, they could have lost their foothold in the industry for sound. As it is, I think companies like QSC have made serious inroads on it (QSC often boasts selling more processors than Dolby).
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 10-21-2018 07:57 PM
Not at all. But new for new sake is a waste of everyone's time and money. If the advantages can't be realized, it is no different than not doing it at all.
As to how long the processors survived. The CP50 was in production just shy of 10-years. When it went into production, the VCAs were discrete components and had to have the transistors mechanically coupled to keep their heat similar and they were not the best VCAs on the planet. The CAT64s were holdovers from earlier products ("E2"). Even still, that product had about a 10 year run. It gave way to the CP55 that was a major upgrade in most everything. The VCAs were better, the CAT64Bs were quieter and removed the input/output levels that could cause more noise, the CAT150 reved to the "C", as I recall which went to a better delay board. The entire control system was MUCH MUCH more friendly to the automation systems of the day (the CP50 was really designed for a manual booth and allowed for pass-through of an existing 4-track mag system...without ANY processing). The CAT240 was also a step up on the CAT108 and put the transformer on the card itself. Componentry allowed for putting both noise reductions on a single card which allowed for more inputs on the B-chain card (a card that didn't exist, really in the CP50 unless you call the CAT112 switch card the B-chain.
That carried us to the CP65...a product that likely wouldn't have come out if it wasn't for Digital audio. But what were the BIG changes in the CP65? hmmmm...transformerless optical preamp (CAT240A) but otherwise the same design...the allowance for Dolby-SR (due to the aforementioned digital audio needing a suitable fallback) and that's it. Mind you, I'm happy that Dolby SR made it to cinema. It was a vast improvement over Dolby-A BUT without proper SR decoding, it sounded worse than A undecoded. The CP65 , I'm pretty sure, had a longer run than 12 years. Sam would know better than I but it had a long run.
The CP500...we'll that was Dolby's first tip-toe into DSP for a cinema processor...what was it running, 18-bit? And it was right on the edge since day one...slot J14, sooner or later would give you an error and merely swapping cards around to get one with better timing in that slot would "fix" it. That got us to the CP650...which had a run for more than 12 years.
As technology matures and an industry gets what it needs, the need for new things decreases unless some new format comes along. Even in film projectors...you can see where the various companies...I'll use Simplex...had quite a few changes early on...but by about 1950 (1948 for Simplex), that was essentially it. The XL was out and all further changes (except for the Apology) were merely shifting things around to make room for a turret or so but the basic projector didn't change...95% of the parts of an XL can be used on a Millenium.
In the case of the DCinema audio...it is delivered in PCM, which is high quality and brand free (in either 48 or 96KHz though I'm unaware of anyone not using 48KHz). So, for DCinema, no A/D is needed...just volume, EQ and D/A. You don't even really need a "Cinema Processor" for that. But Dolby, in the CP750 have put together a package that has the features that MOST cinemas would want (even if they get them in another product...basically, those features are present). If they came out with another product, what would it have? Sonically, unless they got into things like the Trinnov or Datasat where they are taking over the tuning/time alignment, there isn't going to be a need, at THAT LEVEL for a new product. In a cinema environment, what you do to improve the sonic quality of the CP750 (again, unless you get into the tuning itself) is not going to be perceived by 99% of the movie goers. That is, new for new sake would be a waste of everyone's time and money. By the time the CP750 came out things, digitally had matured quite a bit as compared to the CP500 and even the CP650. And, again, it isn't targeted towards the esoteric market where sales are quite limited.
As I have said before, Dolby has done best when the box contains some of their proprietary technology. The CP750 really doesn't even have that. It basically has the Dolby brand trust associated with it. I personally prefer that each button represents an input rather than a format (JSD series) so Digital 1 can be 5.1, 7.1, Pro Logic...etc. With something like the JSD series, you have to consume option button for 7.1 and 2.0 formats. It's a different philosophy.
Personally, I see more and more of our systems moving towards drag-n-drop DSP and that likely means QSYS. But, if you just want to run standard Hollywood fare, the CP750 is a respectable unit that will deliver. You then have your options on what you want to do about speaker crossovers or monitors.
Then again, for all I know, they'll have a new processor at ShowEast this week! (I really don't know).
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![[Roll Eyes]](rolleyes.gif)
Well, I'm sure something positive can happen there too like less heat, less wasted power... and heaven forbid... better power supply reliability! ![[Cool]](cool.gif)
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