Film-Tech Forum ARCHIVE: Format 42

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Posted by Scott Norwood (Member # 30) on 02-09-2008, 06:19 PM:

This is probably a stupid question, but what is the purpose of having two discrete subwoofer channels in format 42 (and 43)? I'm curious as to the reasoning behind the need for this.

Actually, since I've raised the issue already, what is the purpose of having a discrete subwoofer channel at all in any sound format? Why not just let the cinema processor deal with the subwoofer crossover issue just as is done for optical sound? Is there some reason why a user-defined crossover frequency is a bad thing?

Posted by Ron Funderburg (Member # 4561) on 02-09-2008, 07:51 PM:

the director and sound editor determine when a sub-wolfer is to be used to fulfill the two purposes for having a sub-wolfer in the theater. 1st the sub-wolfer moves air so that you feel the sound and second so you hear the sound they intend.

A sub-wolfer in a theater is not there to have sound outside the frequency it is designed to handle pumped in to like some trunk mounted unit in a car playing all the sound though it no matter if it is right sound or not.

The reason for having more than one sub-wolfer is to move more air with less effort never taxing the units! You almost always need two or more subs!

The sub-wolfer function being handled by the processor in optical sound is because there is really no other way to do it with just two discrete channels. You set your base threshold and every thing that frequency or below is pumped to the sub.

And the sub-wolfer really isn't a discrete channel even in digital it is the point one channel of 6.1 and is piggy backed on the surrounds in DTS

Posted by Gordon McLeod (Member # 33) on 02-09-2008, 08:57 PM:

I don't understand how rons anwser fits scotts question on format 42 and 43
on analogue formats it realy is not a sub woofer channel but as its name implies Bass Extension
It started out as many stage speakers didn't go down all that low in response and there purpose was to extend there response below 100Hz which is why they originally had a selectable filter that was set to match the cutoff point of the stage channels

In optical the sub recieves the filter sum of Lt and Rt before the NR circuit and it is passed through a downward expander, vca, filter and eq circuit
For format 42 and 43 the low frequency was recorded on Le and Re and summed and passed through the same expander and filter to the sub

The digital sub input doesn't pass through the downward expander and usually uses a different cutoff frequency

From so old notes it was envisoned that the low frequency sections of the LE and Re speakers could agument sufficiently the bass reruirements

Posted by Ron Funderburg (Member # 4561) on 02-09-2008, 09:04 PM:

Gordon you are probable right I concentrated on the second part and not the first part sorry!

Posted by Scott Norwood (Member # 30) on 02-09-2008, 09:46 PM:

Thanks, Gordon. So, the two low-frequency tracks are there for compatibility with existing Todd-AO systems (pre-CP200), rather than because of any real need to have two discrete subwoofer channels? That makes perfect sense to me.

Posted by Michael Coate (Member # 757) on 02-09-2008, 09:56 PM:

Isn't a "sub-wolfer" one who devours a submarine sandwich?

Posted by Gordon McLeod (Member # 33) on 02-09-2008, 10:04 PM:

On the cp100 with out the SA5 adapter for format 42 one unplugged the eq cards for Le and Re and plugged in a filter card
The CP100 didn't have a sub out
The Eprad Super StarScope was done the same way

Posted by Steve Guttag (Member # 268) on 02-09-2008, 10:17 PM:

Gord got it mostly right and Ron merely spouted what he thinks he knows.

As Gordon said...it was/is called Bass extension or Bass enhancement.

The first incranations of the BE was in 70mm theatres that had 5-stage channels. There was NO subwoofer requirement. The idea was to improve the bass response however and often using the same speaker types as used by the remaining stage channels. That is, the Altec A4 (the most popular, by far, for 70mm theatres. The A4 (as well as the A2 or A1) can go down to 40Hz pretty comfortably, depending on vintage if the bass-wings are installed.

By doubling the track (since they weren't going to use it for a discrete dialog/music) one effectively doubles the power handing and potential bass enhancement of the system. As Gord, noted, it does not need Dolby noise reduction, but uses downward expansion. It also goes as high in frequency as...anyone...anyone...Bueller?...anyone? 250Hz. Clearly not the stuff for subwoofers there. It idea was that one could effectively pan the bass around a bit too. Picture Raiders of the Lost Ark with the big ball rolling across the screen...a panned bass track would add to the illusion on screen. It isn't that bass is non-directional but it is less directional as one goes to lower frequencies. Who here can't tell where the subwoofers are located in a theatre just by listening? I don't know about the rest of you but I sure can and if the bass track goes up to 250Hz, then it is quite directional.

The subwoofer really didn't gain in popularity until about 1980 with the CP200 and even then I was still seeing many A4s or even A5s used in the LC/RC spots. Think about the "subwoofers" of the day in the 1970s and early 1980s. There were few real choices out there.

The CP200 probably handled the whole bass extension/subwoofer thing the best. You installed what you had including both LC/RC as well as subwoofers. One has the option of "telling" the CP200 that subwoofers were in use and thereby limiting the Le/Re channels to the 100-250Hz range with the subwoofer taking over at 100Hz and below. Some connected their subwoofers to the Le/Re outputs though few if any "subwoofers" can give frequencies up to 250Hz justice. A modification for the Cat160, first brought about by THX, came out that would extend the subwoofer output to 180Hz if one did not have LC/RC channels.

When the Cat560 came out, not only that was standardized but the signal that would have sent optical information to the Le/Re channels was killed. OBE was never mixed with Le/Re in mind and as a result, often had the system seem too bassy.

Optical bass extension was always somthing that really should be planned for in the recording. I've played some films that clearly were not (1980s) and with the subs on...things got rather muddy. The OBE circuit has a downward expander and will exaggerate the bass if the signal was not recorded on the film compressed. OBE was also always an augmentation to the main channels and not as a dedicated bass channel like in 70mm and now digital.

So Scott, it has more with the evolution of the subwoofer in main-stream cinema than anything as to why subs are handled the way they are. For most sound reinforcement, subwoofers merely extend the bass range of the system. Even IMAX uses their subs that way...there is a crossover there to take a signal on one of the 6 discrete channels and send that which is below the crossover point to the subwoofers. There is nothing to stop an exhibitor from putting subwoofers on all of the stage channels and adding crossovers to extend their range...however films are not mixed to that. ANSI/SMPTE 202M pretty well defines the response of cinema stage channels.

Steve

Posted by Tim Reed (Member # 137) on 02-10-2008, 03:18 AM:

Scott, are these the "baby booms" you're talking about? Le and Re screen channels?

FWIW, with CP-200's, you also have to watch your "P's" and "Q's". [Big Grin]

Posted by Mark Lensenmayer (Member # 134) on 02-10-2008, 07:59 AM:

Did this have anything to do with Warner's MEGASOUND process?

Posted by Louis Bornwasser (Member # 3063) on 02-10-2008, 08:00 AM:

Somewhere around here I have a copy of the THX modification to the CP-200 for subs......no more "baby boom." (Too many mods on that poor CP-200.) Louis

Posted by Andres Briano (Member # 4621) on 02-10-2008, 09:15 AM:

The source of the subwoofer signal in the Imax format is all 6 channels summed together and not just one. Then it goes through the crossover.

Posted by Bruce Hansen (Member # 281) on 02-10-2008, 11:20 AM:

Isn't "42" the answer to "life, the universe, and everything", as stated in "Hitchhikers Guide to the Galaxy"? [Big Grin]

Posted by Steve Guttag (Member # 268) on 02-10-2008, 11:58 AM:

Sorry...I didn't mean to imply that only one channel has the bass information in IMAX...though I can see how it could be read that way. Yes, any of the six channels can feed the subwoofer if the signal is below the crossover point.

Steve

Posted by Scott Norwood (Member # 30) on 02-10-2008, 12:14 PM:

Thanks to all, especially Steve.

Tim: I thought that "baby boom" was just another name for format 42. Or is it something different entirely?

Posted by Michael Coate (Member # 757) on 02-10-2008, 07:53 PM:

quote: Steve Guttag
The subwoofer really didn't gain in popularity until about 1980 with the CP200...

quote: Mark Lensenmayer
Did this have anything to do with Warner's MEGASOUND process?

It's worth noting the four MEGASOUND productions were released within one year of the introduction of the Dolby CP200.

Posted by Tim Reed (Member # 137) on 02-10-2008, 08:30 PM:

quote: Scott Norwood
Tim: I thought that "baby boom" was just another name for format 42. Or is it something different entirely?

Oh, you're probably right. That's why I was asking. [Wink]

As Louis mentioned, there were a lot of mods for that processor, so I don't know if the Le and Re assignments were later changed (format 42 - 70mm with mono surround).

Posted by Gordon McLeod (Member # 33) on 02-10-2008, 10:11 PM:

For Altered States Mega Sound used EvenTide clockwork sub bass generators

Posted by Sam D. Chavez (Member # 1841) on 02-11-2008, 10:09 AM:

The Bass generators were on the record end. The playback system was unchanged although extra real subs were installed in addition to the LE RE speakers if the cinema had them.

Posted by Gordon McLeod (Member # 33) on 02-11-2008, 10:48 AM:

At the University theatre in Toronto for Altered States there was a eventide unit with 4 amps in a portable rack for the extra subs that were added to the existing CP100/SA5 system there

Posted by Robert Throop (Member # 61) on 02-11-2008, 12:18 PM:

I seem to recall that the Ziegfeld in NYC had an Eventide Harmonizer. Was this for additional surround delay? They didn't play Megasound.
Bob

Posted by Dan Sherlock (Member # 4663) on 02-12-2008, 08:28 PM:

Megasound is described in US Patent 4,110,017. It is similar to Dolby's "Baby Boom" but uses a technique similar to that provided by the old dbx "Boom Box" subharmonic synthesizer. Existing bass frequencies are sampled and divided by half in frequency to create an additional lower octive of sound.

-Dan

Posted by Sam D. Chavez (Member # 1841) on 02-12-2008, 11:30 PM:

Interesting. I did a couple of 70MM previews of this film, one in Vancouver and one in San Francisco as well as setups before the openings.

All these had additional Amps and Cerwin Vega Subs but no extra electronic hardware. I always wondered what the fuss about Mega Sound was all about

Posted by Michael Coate (Member # 757) on 02-13-2008, 07:23 PM:

quote: Sam D. Chavez
I did a couple of 70MM previews of this film...

Sam: By "this," am I correct to assume you are referring to "Altered States" (1980)? There were other Megasound titles, hence my request for a clarification.

Posted by Louis Bornwasser (Member # 3063) on 02-13-2008, 09:02 PM:

I'm with Sam on this one. My tests (Altered States) used conventional Dolby equipment and big amps....& baby boom. Louis

Posted by Sam D. Chavez (Member # 1841) on 02-13-2008, 11:43 PM:

Yes to Altered States

Posted by Martin Brooks (Member # 1269) on 03-02-2008, 07:22 PM:

Altered States at the now-defunct Loew's Astor Plaza was a great experience.

As for format 42, let me see if I can state it a little differently, which hopefully will lend some additional clarity.

Before Dolby, the later 70mm mag films didn't really do a discrete mix across all 5 screen channels. They mixed for 4-track and combined Left and Center and Center and Right and put that into the Left Center and Right Center channels.

Dolby decided that was a waste of those channels and in the Baby Boom format, decided to send Low Frequency ( less than 200Hz) info there. Star Wars (70mm) was the first film in this format.

For the roadshow presentations of Close Encounters, some theatres installed a B Chain with 8 Cerwin-Vega "baby earthquake" subs and 21 Bose 901 surrounds. I saw it at the Ziegfeld where I don't think they added surrounds, but they did add the subs and it was quite an experience. Seeing the "special edition" of Close Encounters a few years later was not as great an experience.

When Megasound was used for Altered States (1980) at the Village Theatre in Westwood, i believe they used the Cerwin-Vega L36PE subs.

I don't believe the CP200 was released until May of 1980, which seems strange to me in retrospect because I believe it would have been necessary for split surround. I no longer remember whether the CP100 could have supported that format.)

Apocalypse Now was the first commercially released film with split surrounds (Format 43) (Superman had some experimental sequences with split surround). That was released in November, 1979.

Low frequencies in channels 2 and 4 were still sent to the Baby Booms, but high frequencies were also recorded into those channels and sent to the split surrounds combined with low frequencies from the mono surround track. There were low pass filters at 250Hz for the baby booms and high pass filters at 500 Hz for the surrounds from channels 2 and 4 and a 500 Hz Low Pass filter from track 6 to the surrounds.

Posted by Bobby Henderson (Member # 840) on 03-02-2008, 07:34 PM:

I thought Format 43 was backward compatible with Format 42.

The way I understood it, from Apocalypse Now being an example, a Format 43 mix on 70mm had three screen channels and three other channels pulling double duty for Formats 42 and 43. The LS and RS channels for Format 43 also had the LFE audio for Format 42. And the Mono Surround channel for Format 42 had the LFE audio for Format 43. Wasn't that how it worked?

Posted by Sam D. Chavez (Member # 1841) on 03-02-2008, 08:54 PM:

"I thought Format 43 was backward compatible with Format 42.

The way I understood it, from Apocalypse Now being an example, a Format 43 mix on 70mm had three screen channels and three other channels pulling double duty for Formats 42 and 43. The LS and RS channels for Format 43 also had the LFE audio for Format 42. And the Mono Surround channel for Format 42 had the LFE audio for Format 43. Wasn't that how it worked?"

The missing link is the Dolby SA5 unit whipped up for Superman and Apocalypse Now. It worked with the CP100 to provide split surrounds as well as 1/3 Octave EQ for the surrounds.

The Low Freq. info on channels 2 and 4 went to the subs after processing, the above 250 Hz Channel 2 was combined through a filter with the channel 6 low freq. mono surround info and went to left surround; channel 4 above 250 Hz info went to right surround as in the previous sentence.

Channel 6 or rear surround use was optional on screens equipped for left and right surrounds, but was very useful as it provided a 6 track mix for screens without Stereo surround capability.

Posted by Tim Reed (Member # 137) on 03-02-2008, 09:01 PM:

You really had to watch your "P's" and "Q's" with that setup. [Razz]

Posted by Michael Coate (Member # 757) on 03-03-2008, 04:31 AM:

quote: Martin Brooks
Apocalypse Now was the first commercially released film with split surrounds (Format 43) (Superman had some experimental sequences with split surround). That was released in November, 1979.

November??? Neither one of those was released during that month!

"Superman" had a nationwide, saturation release in December 1978. "Apocalypse Now" was released in Los Angeles, New York and Toronto (on a guaranteed-seat, pseudo roadshow basis) on August 15, 1979. A handful of other major markets started their runs in September, and the nationwide launch began Oct. 10, 1979.

(I guess you could say "Apocalypse" was in release during November of '79!)

Posted by Steve Guttag (Member # 268) on 03-03-2008, 05:59 AM:

Sam was close...500Hz was the "Crossover" point for the surrounds. Tracks 2 and 4 provided the stereo surround information above 500Hz and track 6 provided a mono surrond information below 500Hz for format 43 capable theatres. Those that could play only format 42 would send track 6 (Which was recorded full-range) to the surrounds as normal and 250Hz and below from tracks 2 and 4 to Le/Re as normal.

This gap between the 250Hz bass and 500Hz HF for surrounds ensured no bleed through on the track. Also, the 500Hz crossover was convienent as most all speaker systems for cinema at the time were 2-ways and almost all had 500Hz crossovers. As such, a Non-Dolby 70mm theatre (and they did indeed exist into the 1980s) could merely disconnect their HF drivers on Le/Re speakers and play a format 43 film with or without NR (I've seen some venues that had 6 Dolby 361 NR frames).

So, as you can see, format 43 was indeed very backward compatible to existing systems and as such, a very clever format given its past and what it was expected to do.

The SA5 for the CP100 (see the manual here on F-T) more than resembled a CP50. Think about it...A CP50 has most of what one needs for split surrounds in it... a pair of NR cards, meters for calibration, 1/3-octave EQ and even some control-logic on board. The difference was the Cat 158 which did the stereo surround work. In the SA5 it also had the job of splitting up the bass and sending it out to the 105Ds in the CP100. The CP200 did not use that particular feature but the CP200 did indeed use the same Cat 158.

Steve

Posted by Sam D. Chavez (Member # 1841) on 03-03-2008, 10:19 AM:

I believe the crossover point was lowered later to 250 Hz by use of sharper filters, but not so important a point.

Posted by Jeffry L. Johnson (Member # 453) on 03-03-2008, 12:12 PM:

Note that the Chronology on Dolby's Web site mentions November 1979 several times.

Dolby Chronology web page

quote:
Six-track magnetic 70 mm prints of _Superman_ were used in presentations with "stereo surround," that is, separate Left and Right Surround channels rather than the usual mono surround track. This development, the forerunner of today's 5.1-channel format, was made public for the first time in November 1979 with the release of _Apocalypse Now_.

quote:
November 1979
Dolby Stereo 70 mm format with stereo surround publicly announced with release of _Apocalypse Now_, showing in 15 theatres equipped for this forerunner of today's 5.1 format.

Posted by Michael Coate (Member # 757) on 03-03-2008, 05:11 PM:

Dolby's Company Chronology is full of errors, often in cases where numbers and dates are cited.

Saying they "made public" or "publicly announced" the split-surround format during November 1979 sounds like a bizarre issue of semantics. Or is it meant to imply the company issued a press release during that month? At any rate, by November, "Apocalypse Now" had opened in all of the major North American markets.

quote:
November 1979
Dolby Stereo 70 mm format with stereo surround publicly announced with release of _Apocalypse Now_, showing in 15 theatres equipped for this forerunner of today's 5.1 format.

I'm aware of 16...but who's counting! [Wink]

quote: from an aborted project of a few years ago

08.15.1979 ... Los Angeles, CA: Cinerama Dome
08.15.1979 ... New York, NY: Ziegfeld
08.15.1979 ... Toronto, ON: University

09.21.1979 ... Newport Beach, CA: Newport
09.21.1979 ... Orange, CA: Cinedome
09.21.1979 ... San Francisco, CA: Northpoint
09.21.1979 ... San Jose, CA: Century 22

10.03.1979 ... Washington, DC: Uptown

10.05.1979 ... Calumet City, IL: River Oaks
10.05.1979 ... Chicago, IL: State-Lake
10.05.1979 ... Evergreen Park, IL: Evergreen
10.05.1979 ... Montreal, QC: York
10.05.1979 ... Niles, IL: Golf Mill
10.05.1979 ... Oakbrook, IL: UA Cinema
10.05.1979 ... Vancouver, BC: Stanley

10.10.1979 ... Boston, MA: Cinema 57

Plus, key international bookings in Paris (09.26.1979), Sydney (11.15.1979; Hoyts), London (12.01.1979; ABC Shaftesbury Avenue), and Tokyo (03.15.1980). It was also screened by special arrangement at the Moscow Film Festival in August 1979.

Posted by Louis Bornwasser (Member # 3063) on 03-03-2008, 06:30 PM:

FYIW: I installed the SA-5 at the Uptown in DC. Also reactivated the amps and speakers left over from Sensurround, fed from the SA-5. Really big thump on Apocalypse Now. Louis

Posted by Sam D. Chavez (Member # 1841) on 03-03-2008, 08:08 PM:

Superman was a Beta site for split surrounds and was not announced or promoted. Apocalypse Now was the feature for which this split surround process was engineered. Dolby and Zoetrope were right around the corner from one another back then and Tom Scott, Walter Murch, and Mark Berger who later went on to win awards for sound were in constant consultation.

Century 21 was the San Jose location, not 22. I know because I was there every day working with Zoetrope for RCA Service, just before moving over to Dolby Labs.

Posted by Michael Coate (Member # 757) on 03-05-2008, 01:52 AM:

I can't believe Dolby Labs and/or United Artists didn't foot the bill for the install of the SA5.

quote: Variety; Aug. 31, 1979

70mm 'Apocalypse' Equipment Costly For Exhibitors

Theatre operators who will be screening the 70mm version of Francis Coppola's "Apocalypse Now" in the suggested Dolby "surround sound" format will be asked to fork over almost $4000 for the necessary equipment. Coppola reportedly delayed the United Artists release until he could perfect the "quintaphonic" wraparound soundtrack for dialog, sound effects and an electronic-rock music score.

Dolby Laboratories Inc., San Francisco-based as is Coppola's American Zoetrope Co., designed the Dolby SA5 surround adapter specifically to enable playback of separate left and right (stereo) surround information contained on the 70mm magnetic prints of "Apocalypse Now."

To use the adapter, an exhibitor must already have Dolby model CP100 stereo units, equipment most houses with the capability to show 70mm pix already possess.

UA marketing veep Robert L. Friedman said some 15 theatres are eventually expected to play 70mm versions of "Apocalypse," including the three situations now showing the credit-less version of the war epic in New York, Los Angeles and Toronto. UA is not picking up the tab for any of the special Dolby equipment needed in the 70mm engagements, said Friedman.

In printed instructions to exhibs, Dolby noted that "Apocalypse Now" is "particularly demanding of the theatre sound system, as are an increasing number of Dolby Stereo 70mm releases."

Track configuration of the stereo surround format used for "Apocalypse" differs only slightly from other 70mm Dolby prints, primarily in having five distinct sound tracks. In addition to the usual left, center and right screen speakers, system uses extra left and right screen speakers, as well as a second surround power amplifier and the special SA5 surround adapter.

Basic cost for the latter unit is $3700, with three options available that could bring the total price to almost $5500. Provisions are also made for trade-ins on now-outmoded Dolby equipment.

Dolby also notes that "while the special directional effects created for 'Apocalypse Now'...will not be reproduced with conventional Dolby Stereo playback, the film will sound as good as conventional Dolby Stereo 70mm releases when played without the SA5."

Posted by Sam D. Chavez (Member # 1841) on 03-05-2008, 10:35 AM:

I remember all that.

Zoetrope kept altering the mix to what would playback in a very good cinema. I saw the Napalm and strafing scene perhaps 50 times with subtle (to me)differences based on what the speakers could handle at the Century 21 San Jose. This was also going on at the Nothpoint IN SF.

This was a house with A4's, added subs, and three banks of A7's on Left surround, Right surround, and a Rear surround channel. This arrangement worked very well on a dome stadium house.

This Cinema had an 8 channel Ampex system with the 120 Watt Ampex amplifiers spread over 5 racks. The amps were deemed too noisy and unreliable and were replaced with of all things, TOA amps (Yuk) that were considered good for their day.

Posted by Tim Reed (Member # 137) on 03-05-2008, 09:26 PM:

OMG, TOA's! [puke]

FWIW, didn't the SVA version of "Apocalypse Now" have no surround information at all? For some reason, I'm thinking that and "Xanadu" were a couple of the rare Format 03 pictures.

Posted by Bill Gabel (Member # 1105) on 03-05-2008, 09:39 PM:

When I saw "Xanadu" first run at the Mann's Chinese twin theatres in Hollywood, there was a surround track.

Posted by Sam D. Chavez (Member # 1841) on 03-06-2008, 12:07 AM:

There is always a bit of a "magic" surround track, but the matrix was not as discrete as it is now and the director or head sound mixer would deem what was leaking out to the surround unusable and ask it be turned off. Problem was the cinema always wanted the surrounds throbbing off the walls.

Funny, the Apocalypse people actually put a letter in the film can asking the surround power amp be turned off. There were a lot of 2 channel Crown amps back then and techs tended to use one amp for the center and surrounds, so guess what happened?

Murphy Law.

Posted by Mark Gulbrandsen (Member # 72) on 03-06-2008, 07:28 AM:

I saw A.N. at the UA-150 in Oakbrook... the place always sounded like the eq was way off... no bottom end from the day it opened to the day it closed... strange for such a big place... Excellent picture though with Super Cinex's and DP-70's.

Mark

Posted by Mitchell Dvoskin (Member # 751) on 03-06-2008, 08:30 AM:

35mm original release prints of Apocalypse Now "officially" had no surround. The helicopter attack scene did indeed have outstanding surround, but that was it. The story at the time was, and I don't know how true it is, was that the sound mixers added the surround for that sequence on their own, without studio/Coppala approval.

Xanadu was Dolby A stereo with surround.