This is topic DFP3000 levels in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.


To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=006275

---

Posted by Antonio Marcheselli (Member # 373) on 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
 

---

Posted by Michael Schaffer (Member # 1204) on 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.
 

---

Posted by Antonio Marcheselli (Member # 373) on 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
 

---

Posted by Christos Mitsakis (Member # 143) on 06-18-2004, 10:14 AM:
 
Antonio,
SDDS 0.0 dB = "7" on 650 and all Dolby processors (-20dBFS).

Christos.
 

---

Posted by Antonio Marcheselli (Member # 373) on 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
 

---

Posted by David Graham Rose (Member # 1450) on 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
 

---

Posted by Gordon McLeod (Member # 33) on 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
 

---

Posted by Antonio Marcheselli (Member # 373) on 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
 

---

Posted by Michael Schaffer (Member # 1204) on 06-18-2004, 08:28 PM:
 

quote: Antonio Marcheselli

---

SDDS' Left Channel 0dB = Dolby's Left Channel ??

60? 70? 100?

---