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Author Topic: Definition of "Mono Compatible"? Sean McKinnon Phenomenal Film Handler Posts: 1712 From: Peabody Massachusetts Registered: Sep 2000 posted 02-20-2008 03:24 PM                        Here is the million dollar question. In those circa 1980 era mono houses taking into consideration the quality of the speaker, A-Chain, Amplifier etc... Would a sound mixing engineering golden ears audiophile proffessional find an "academy mono" optical track acceptable? In order for the Dolby nr track to sound acceptable you would have to take into account wether or not the mono track did? Note that I am making no statements as to wether or not certain systems were adequate or sounded good, or bad. I am only posing the question because unless the system sounded 100% perfect when playing back a mono print, it is unfair to blame the Dolby nr track for not "sounding good"  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 02-20-2008 05:33 PM                        The "not sounding good" that I am talking about here is irrespective of the quality, either good or bad of the B-chain --the speaker system, the amp quality or anything else in the playback system. I am talking specifically about the noise reduction process. Sure, if the mono system sounded like crap to start with, then that's the system. But I am just talking about what Dolby A (or SR) noise reduction sounds like when it is not decoded properly or in this case, is not there at all; forget about the rest of the parameters. Dolby n/r is an ACTIVE, dynamic process that will definately be heard if there isn't the opposite, complimentary process compensating for it in the playback in real time. That is why we take so much care making sure the Dolby level is matched correctly, because even a slight mistracking can be heard. But with the so-called mono compatible business -- just playing a Dolby encoded print on a system without ANY tracking whatsoever....it just doens't make sense to say that's acceptable. I doubt anyone here would claim that playing a Dolby print on a processor where the Dolby levels were totally out of wack would "sound OK." How can anyone claim that having no processing at all would be even marginaly acceptable?  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 02-20-2008 07:10 PM                     Oh, pretty easy Frank. You can't compare the effects of NR in a full fidelity tape recording to the effects of NR in an optical mono system. In a tape or other wide-band system, you will hear the compression artifacts pretty easily, particularly in the HF and you may even hear them in the LF though people's hearing is not as well tuned into those areas. In a cinema system for optical mono, we have a frequency response of somewhere around 100Hz to about 4KHz. In some sytems you might get the bottom end down to 60Hz or so...depending on room and speaker. So in the case of Dolby-A, you can throw out the artifacts of the 1st and 4th band...they simply are not being reproduced at any level to begin with. This leaves you with 10dB compressors in the two remaining mid-band areas. Mono films are inherently compressed to fit within the VERY limited dynamic range of the optical track. So what is left to the artifacts boils down to some compression artifacts in excess of what would have been done with a fixed rate compressor. It isn't like the tracks were being recorded uncompressed to begin with. Can you pick out the compression artifacts? Sure. But you can do that with ANY type of compression, not just variable. People seem to listen to radios and even MP3s and they have no resemblence to what was actually recorded in the studio. However, a benefit of a Dolby-A encoded film in a Mono theatre is often an improved HF response since the HF is compressed to a greater degree than the other bands. Again, you are NOT reproducing the audible range (20Hz to 20KHz) in a mono theatre so the effects of the Dolby-A encoding are not nearly as perceptable and have PROVEN by a VAST MAJORITY of audiences to be quite acceptable...or as some would say, "compatible." Does the sound of Dolby-A in a mono theatre bother you? I can believe that...but what percentage of people watching movies have the background and experience you have to even notice what a compression artifact sounds like? They hear that stuff every day in other audio forms and don't know any different. Now your example of playing a miscalibrated decoder not sounding right is another story. In that case, the room has been tuned for a wide-band response. 40Hz-12.5K at the worst and possibly out to 16K but the perfs in the screen are going to make things progressively more difficult to sound natural above 9KHz. So in this case, you don't have the masking effects of a poor sound system tuning (hopefully) and you combine that with what should be a complimentary expander. If miscalibrated, you get will get pumping and all sorts of compansion artifacts that also result in very unflat responses too. Those are much more easy for the layperson to pick off. You have this active device actively fiddling with the sound incorrectly and the system is reproducing this mess beautifully. Note, if you were to take a good cinema processor and just bypass the NR cards but let the rest of the system stand, you too would find the compression artifacts more annoying than on a band limited system. What I personally find much more of a problem is playing back Dolby-SR tracks with ANYTHING but real Dolby-SR. Dolby-A sure doesn't work well, fake Dolby-SR (Cat 222SR/A) doesn't work well either. Most SR emulators (well all except Pana's CM-353 and Dolby's CP650) really suck too. Yet I've seen countless systems that upgraded to digital but didn't do a thing for their NR system for analog. The thought being, I guess, "well it is just the backup track anyway." I do find it odd that you find the mistracking of playing back Dolby-A films in a mono sound system to be so offensive but don't seem to mind the horrible vertical displacement of using a cluster speaker to play back a film on a non-perf screen. Psycoacoustically, that just never works for me and many others. The image just doesn't match the sound (Depending on just how far separated it all is). Then again, hard-center dialog doesn't work for me either...very distracting...particularly on scope films. Steve  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 02-22-2008 12:22 PM                       Okay, Michael's search for facts has me wondering about something. I was a projectionist in a repertory house in the late 70s and early 80s. We had a CP-50 and were full-stereo. We must've played 14 different films a week on our single-screen; a mixture of old and newer pictures, so we got a lot of stereo and mono prints. If we received a MONO PRINT of a movie that had a Dolby logo in the credits, I always played that movie with the NR ON. Whenever I tried to play a "non-Dolby" movie with NR ON, it sounded hissy. However, it seemed to work fine on "Dolby" movies and sounded just as clean as their stereo print counterparts. I always thought that was standard practice on Dolby pictures (but don't ask me how I came to that conclusion). Was this wrong of us to do? Sam?  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 02-23-2008 04:06 PM                       Tim, There was very little in the way of Dolby Mono films after 1974 and only a few in total before Stereo took hold. I assume you were just using the NR button and not all of them. You could generally tell whether the film was Dolby encoded as the tracks were literally smaller as the average modulation level was lower and dubbing guys were more careful not to over modulate or clip the tracks. The encoding equipment provided by Dolby gave warnings in the way of metering and red clip lights to let the mixer know when he/she was clipping the tracks. Clipped Mono tracks sound pretty horrendous played back in Dolby Stereo as there was not generally near the care taken making Mono tracks. Job one was to get the tracks as loud as possible to get over the noise and scratches. Now that this thread and Frank have cooled down a bit, I wanted to say that A type NR was pretty gentle and worked mainly on the soft parts of the soundtrack and not on the loud parts which is mostly all there was on Mono film recordings as stated previously, and why you could "get away" with playing back encoded tracks with no decoding. There were other forms of NR around, the most popular was the DBX which was straightforward compression on record and expansion on playback. Playing back with no decoding was unmistakebly nasty. Very few DBX recordings made to cinemas except on Sensurround features and trailers. There was no mistaking when the DBX was mistracking. It literally pumped like an old Pipe Organ. [ 02-23-2008, 06:07 PM: Message edited by: Sam D. Chavez ]  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 02-23-2008 08:01 PM                       Hi, Sam! Thanks. Yes, just the top two buttons IN on the CP-50 for mono prints of Dolby movies. I know the familiar diminuitive appearance of the Dolby-encoded track you describe, although it's been too long to recall if the mono prints looked that way, too. I only remember seeing the soundtrack area of the leaders go: REEL 5 MONO REEL 5 MONO REEL 5 MONO REEL 5 MONO And, of course, a stereo print of that same movie would say: REEL 5 STEREO REEL 5 STEREO REEL 5 STEREO REEL 5 STEREO Whereas, a regular mono print (with no corresponding stereo version in existence) would simply say: REEL 5 REEL 5 REEL 5 REEL 5 REEL 5 REEL 5 (Color by Movielab)  |  IP: Logged Robert Harrison Expert Film Handler Posts: 239 From: Harwood Heights, Illinois, USA Registered: Jun 2005 posted 02-24-2008 01:22 PM                     Here is an excerpt from an article from the year 1981, "Mixing Dolby Stereo Film Sound" from an issue of Recording Engineer/Producer: ...Thus Dolby Stereo prints are physically compatible with standard mono projection equipment, and it was originally claimed that they would play equally well in stereo and mono. Experience has shown that physical compatibility is not sufficient, however. As we shall see, the mix on the stereo tracks determines how well they will play in mono. Lately, distributors have been increasingly interested in the economy of a single-inventory release -- that is, supplying only stereo prints to mono and stereo theaters. (Such films as Star Trek, The Empire Strikes Back and The Jazz Singer are good examples of this sort of release.) Although mono mixes were made for foreign language dubs, stereo prints are in general domestic circulation. Compromises in dynamic range and stereo width must be made in the stereo mix, to insure compatible mono replay of stereo prints. Here are some thoughts on the matter from Bill Varney: "I find that when you play a Dolby two-track Stereo optical print on a mono projector, the sides tend to pile into the center. If in the dub you have a lot of high-energy material working out there on the sides, in stereo it may not in any way encumber the dialogue or whatever is coming out of the center, because of the spaciousness of what's happening. It might, however, do it in mono. "There also seems to be a severe loss in the high-end, and I notice a relatively large increase in the low end. These two factors tend to make it sound very muddy. The fact that you are working with a Dolby-stretched signal is not, generally speaking, quite enough to counteract the sharp Academy roll-off." Dolby film consultant Tom Scott notes the similarities between making mono compatible record and film mixes: "If your stereo film mix is intended to be mono-compatible, you have to follow somewhat the same rules that you do when you're making a mono-compatible stereo record. You need to be careful of anything placed exactly in the phantom center. For example, on a stereo record you may have the bass, snare drums, and vocal exactly in the center and everything else panned to various places across the two channels. When you add the two channels together, material that is in the phantom center will combine and be 6 dB louder electrically. This changes the balance of the phantom center information to the rest of the mix. "Center information will pop up in mono, which can actually help in films. In general, to get a good mono-compatible mix the dialogue needs to be a little louder in a mono theater; since dialogue is in the center, it will get louder when played in mono. Whether it gets loud enough for a good mono is the question. If you have common information on the two sides, it will try to come out of the center anyway, when you add them together that will also get louder." Ioan Allen feels that "what controls compatibility is not how low the lowest sounds are, but how loud the dialogue is compared to 100% on the track. The monitor level is tied directly into how loud the voices will be made, and how the effects and music are spaced into the room you have left over the voice. If you have set your meters and monitors so you have only 3 dB left to go over the voice level, then the effects will be very low compared to the voice. If you have 20 dB to play with above the voice, then it will be 20 dB louder. By setting the monitor level lower, you force the voice higher. In other words, if your monitor is high, the dialogue is lower and your mono compatibility goes down." When played at the standard relatively soft level used in most mono theaters, low-level dialogue on stereo mixed with excessive volume range may be unintelligible.  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 02-24-2008 06:27 PM                       This last post brings back a lot of memories. Both people quoted were some of the best I had the pleasure to work with and try to learn from. Tom Scott won at least three awards for sound, Apocalypse Now, Right Stuff, and one other that escapes me for the moment. The essential issue about mono compatibility that I believe had Frank all worked up is that he went through the entire process of hearing the original sound and then the end result. Kind of like seeing the cow and then the hamburger that is the last of it. But the audience only ever hears the end result so judges it on its own merit. Can you understand the dialogue was the bottom line on compatibility.  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 02-24-2008 08:11 PM                       quote: Sam D. Chavez Kind of like seeing the cow and then the hamburger that is the last of it. Sam, you're funny. I like the way you put things.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 02-25-2008 10:49 AM                        Steve, that's funny....as I was writing that last post, I was going to say, that some of us here find the displacement of speakers above and on the sides of a screen to be disconcerting, so surely being able to hear the anomolies of an undecoded Dolby track pumping way would be glaringly obvious. I guess the fact that I spent a few years of my life in a studio mastering listening in near-field where one of the most critical issue that we had was making sure the single-ended compression that we had to use was done so that it could not be heard. I because very sensitized to that threshold where a master recording would be rejected because there was too much audible compression. And every cut that was being recorded would need to have a different level of compression too -- certain music could stand more than others. The last thing that you wanted was to hear that damn noise floor breathing. As far as the displacement of speakers -- I don't know what to tell you -- I am just not as attune to it as you. But then again, I have never heard any complaints from anyone about it, not even studio types who rent the place for previews. Which just goes to show you, Joe Moviegoer evidently has a very wide latitude in what he will tolerate, as you point out with with mono-compatible. Then again, because it's tolerated doesn't make it good operating practice. Can anyone say Pan and Scan?!  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 02-25-2008 11:03 AM                       Thanks Tim, sometimes there analogies just come to me, sometimes at inappropriate times. IMHO, humans are not as sensitive to vertical location of the sound image as they are to the horizontal component.  |  IP: Logged Thomas Pitt Master Film Handler Posts: 266 From: Leeds, West Yorkshire, UK Registered: May 2007 posted 02-25-2008 12:30 PM                     If you're running a film in mono when you have a 5.1 system installed, it's best to make all the sound come ONLY from the center stage speaker. That way, the sound always appears to come from the screen, and is less susceptible to echos and 'phantom stereo' caused by having the same signal fed to all speakers. If you're running with a 2-speaker stereo system, the best option is to feed the same signal to both speakers. If you feed the signal just to one, it will sound strangely lopsided and be quite distracting for viewers! Humans are better at detecting horizontal sound position because our ears are level on a horizontal plane. Some animals, like owls, have one ear slightly above the other (on opposite sides of the head) and can therefore detect the vertical position of sounds better.  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 02-25-2008 09:00 PM                       I have one ear slightly higher than the other so I must be an Owl?  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 02-25-2008 09:29 PM                     Well you are certainly a Hoot! Thank you, thank you....I'll be here all week!  |  IP: Logged

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