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Author Topic: DFP3000 levels Antonio Marcheselli Phenomenal Film Handler Posts: 1260 From: Florence, Italy Registered: Mar 2000 posted 06-15-2004 04:26 PM                        Hi everyone. I have a question. I see too many times our SDDS 3000 player goes to "OVER" on the main display. I realize that the channel meters are monitoring the outputs since if I mute the master volume the meters go to zero. So I wonder how I can I prevent the clipping. I thought that during equalization I should compensate the equalization with channel level. Example: I trim Left Channel 1000Hz level to +2dB and I lower the main Left Channel level to -2dB. With subwoofer is simpler since there is only two parametric eq: if I set one eq to +2dB and I set the main channel level to -2dB I should have no problem, isnt' it? The EQ was made this way, but just today I saw "Torque" in extreme clipping mainly on SW channel for MANY SECONDS... At the reference level, of course, no more. Should I left few headroom like, for example, set eq for +2dB at 60Hz and lower the main channel to -4dB? This question call to my mind another one: if in DFp3000 the zero level is "0dB", what is the "zero" level on the CP650? What is the level that, if I apply no equalization, prevent the sound to clip at outputs? Thanks for your replies! Bye A  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 06-17-2004 03:40 PM                        The channel levels are pre-fader, so the fader setting will not influence them (muting is different, as it cuts the channels pre-fader too). If an individual bands is raised by 2dB, it is not necessary to lower the channel level by 2dB. The channel level is the sum of all individual bands which are usually around 70dB, boosting one of them will not have the same effect on overall channel level as on the individual band. As a general rule, it is better to cut than to boost and to make sure neighbor bands are not further than 3dB apart, and not to overdo the equalizing as the bands will never be perfectly flat on the RTA. It is an approximation only anyway. If you cut more bands than you boost and use the amplifier gain control to achieve an overall level of 85dB SPL in the room, then you shouldn`t run into the digital clipping as often. If it still is there, it is best to lower the digital channel level a bit and compensate on the amplifier. The DFP outputs are rather quiet, so you won`t add any perceptible noise by lowering the channel levels a bit. SDDS 0dB = Dolby +20dB.  |  IP: Logged Antonio Marcheselli Phenomenal Film Handler Posts: 1260 From: Florence, Italy Registered: Mar 2000 posted 06-18-2004 08:04 AM                        Hi Michael How is going? Thanks for your reply. I understand that if I raise just only band to +2dB the master channel level should not lower to -2dB. This can have sense if I raise ALL the band of +2dB, right? I showed a preview of Torque at -2.5dB (master level) and in one scene (I was not in front of the processor all the time!) the SW channel clipped for many seconds... (another example is the Cavalcade trailer that clips on the main explosion!) Let's suppose that I left all the channel to 0dB (level and eq). Should'nt I be safe from clipping since the digital records cannot go over 0dB FS? I don't know if this makes sense. SDDS 0dB= Dolby +20dB? Is not -20dB? But what I mean is different: If in SDDS processor the 0dB (both for channels level and master level) is the value that does not change the input signal (let's say I have a 300mV signal recorded, I have a 300mV signal at outputs), what is the same setting for CP650 (channels levels)? And: is this setting the maximum setting that prevents signal clipping on the processor outputs? I really don't know if I was clear. In my experience I found that many installers does not pay too much attention in signal levels this is why I'm asking this! Bye A  |  IP: Logged Christos Mitsakis Expert Film Handler Posts: 242 From: Ag.Paraskevi, ATHENS, GREECE Registered: Sep 1999 posted 06-18-2004 10:14 AM                     Antonio, SDDS 0.0 dB = "7" on 650 and all Dolby processors (-20dBFS). Christos.  |  IP: Logged Antonio Marcheselli Phenomenal Film Handler Posts: 1260 From: Florence, Italy Registered: Mar 2000 posted 06-18-2004 10:20 AM                        Christos, I mean the internal channel's level. SDDS' Left Channel 0dB = Dolby's Left Channel ?? 60? 70? 100? Bye A  |  IP: Logged David Graham Rose Expert Film Handler Posts: 187 From: Cambridge, UK Registered: Sep 2002 posted 06-18-2004 02:23 PM                     Greetings from a wet Cambridge Reference level for stage channels on Dolby Processors is 85dB. Surround levels vary with processor type (82dB on a CP650 for all channels, even in EX, since internal gain controls allow the folding back of the system between EX and standard Dolby Digital). For SPL's of SA10's with other combinations of processor, check the SA10 installation manual, since they tend to vary depending on the CP in use. From Cambridge, Goodnight  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 06-18-2004 04:45 PM                     How do you know it is clipping if memory serves the SDDS display doesn't actually show the level at clip  |  IP: Logged Antonio Marcheselli Phenomenal Film Handler Posts: 1260 From: Florence, Italy Registered: Mar 2000 posted 06-18-2004 07:31 PM                        Hi Gordon Our DFP 3000s have a zero dB point and then a red led that says "OVER". I thought that it means "clip" but you're true, I'm not sure. Can someone confirm? In both cases my question remains: what is the channel level that avoid clipping in the processors? David Thanks for your reply. However I mean the internal channels levels not the level in the auditorium! Bye! Antonio  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 06-18-2004 08:28 PM                        quote: Antonio Marcheselli SDDS' Left Channel 0dB = Dolby's Left Channel ?? 60? 70? 100? 105. Fader SDDS 0dB=Reference level=Dolby 7 One number increment on the Dolby Fader is very roughly 3.2dB (I have a reference chart somewhere, but can`t find it). so SDDS +10dB=Dolby 10 Channel level SDDS reference level -20dB=Dolby 0dB=85dB SPL (theoretical) pink noise Full scale SDDS 0dB=Dolby +20dB You just have to keep in mind that the signal level, Fader level and approx. SPL in the theater are different values. Signal level is what is input into the B chain, the fader controls the output and the SPL results from the fader and gain settings on the amplifier (and the characteristics of the speakers and room etc). Since it is a digital medium, you do not calibrate the input like with analog sound where the gain structure is also influenced by the optical system calibration. The fader should always be set at the reference level and calibrated pink noise either from a card like Cat.85c or CE SG-1 or from the setup software should be used. The actual SPL in the theater results from the channel level setting in the processor and from the gain setting on the amplifier. Some crossovers also have gain settings which influence the overall gain structure. Here in the US I have found it is a very common practice to set the amplifier gain to full and then just work with the channel level. This is mainly to avoid that people tamper with the equipment and blow stuff up because they turn up the gain controls. In Europe, it is more common to find a setting around 2/3 of the amplifier gain and adjust the channel level to that.  |  IP: Logged Antonio Marcheselli Phenomenal Film Handler Posts: 1260 From: Florence, Italy Registered: Mar 2000 posted 06-19-2004 07:50 PM                        HI Michael Thank you, it is what I want to say! Yes, I know what each level means, but I do not fully agree with the common tecnique that use to put at maximum the amplifiers and then set the other levels. Ok, digital outputs of actual equipment is very quiet but I really prefer to set the correct levels in the equipment and THEN the resulting setting on the amplifiers... However I can agree that there is not so much differences and in the first case you minimize the possibility to clip the signal in the processors... Thanks for your help! Bye Antonio  |  IP: Logged Alan Haigh Film Handler Posts: 45 From: Watford, UK Registered: Jul 2003 posted 06-24-2004 03:38 PM                    Hello Antonio You should make sure the channel levels in the set up software are not above 0dB as this can cause clipping if you play the film at reference level. Keep this close to, but below zero, cut EQ frequencies on the whole rather than increase (and make sure the "curve" of the EQ bands looks smooth), and make sure the amps are powerful enough! Also remember that it's not unusual for the film print master to clip occaisionally, so it may be meant to be like this! SDDS has a 1:1 digital transfer from master to film negative. Alan  |  IP: Logged

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