Jump to content


Photo

what is the"dB" means?


  • Please log in to reply
5 replies to this topic

#1 YongLee

YongLee
  • Basic Members
  • PipPip
  • 33 posts
  • Cinematographer
  • P.R.C

Posted 10 June 2007 - 07:36 AM

What is "dB", for example ,dynamic range of HD usual is 72dB.
what difference between the stop and dB?
  • 0

#2 David Auner aac

David Auner aac
  • Sustaining Members
  • 1117 posts
  • Cinematographer
  • Los Angeles

Posted 10 June 2007 - 10:21 AM

What is "dB", for example ,dynamic range of HD usual is 72dB. what difference between the stop and dB?


DB stands for deci Bel. Bel a is measure of the magnitude of a physical quantity (e.g. power) in comparison to a reference level. For example it's used to measure sound pressure in relation to the human hearing threshold. For more info see wikipedia.
In the video world, the dB is used as a measure of signal amplification. When shooting in low light you can use a gain setting to boost your signal to make the image brighter, but that introduces grain because the signal is amplified by a DSP. Six dB equal about one stop. So 72dB would equal 12 stops, if I am not mistaken and it's the same here as it is with gain.

Cheers, Dave
  • 0

#3 Chris Keth

Chris Keth
  • Sustaining Members
  • 4427 posts
  • 1st Assistant Camera
  • Los Angeles

Posted 10 June 2007 - 11:11 AM

Six dB equal about one stop. So 72dB would equal 12 stops,



That sounds like way too much for HD dynamic range, no? Where did the 72 come from, YongLee?
  • 0

#4 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19769 posts
  • Cinematographer
  • Los Angeles

Posted 10 June 2007 - 06:55 PM

That sounds like way too much for HD dynamic range, no? Where did the 72 come from, YongLee?


Due to noise, not all the stops may be usuable, plus some cameras may lop off some of that info before processing/compressing.
  • 0

#5 Matt Sandstrom

Matt Sandstrom
  • Basic Members
  • PipPipPipPip
  • 464 posts
  • Director
  • Stockholm, Sweden

Posted 18 June 2007 - 07:33 PM

you can't translate it into stops like that because it doesn't take clipping into account, nor gamma.

/matt
  • 0

#6 Michael Collier

Michael Collier
  • Basic Members
  • PipPipPipPip
  • 1262 posts
  • Gaffer
  • Los Angeles, CA

Posted 18 June 2007 - 08:19 PM

The 72db rating might be a signal to noise ratio. That would be the measurement of noise (referance level) to signal (dB). The higher the STNR the better, since the higher it goes, the less noise there is compared to signal strength. if that were the case it would be just about right. Most cameras fall between 65-80dB signal to noise range.
  • 0


CineTape

Media Blackout - Custom Cables and AKS

Paralinx LLC

Aerial Filmworks

Visual Products

Willys Widgets

Ritter Battery

Metropolis Post

The Slider

Broadcast Solutions Inc

Tai Audio

Opal

Technodolly

Gamma Ray Digital Inc

FJS International, LLC

Rig Wheels Passport

Abel Cine

Wooden Camera

rebotnix Technologies

Glidecam

CineLab

Media Blackout - Custom Cables and AKS

Broadcast Solutions Inc

Metropolis Post

Willys Widgets

Aerial Filmworks

CineLab

Ritter Battery

Rig Wheels Passport

Opal

Visual Products

rebotnix Technologies

FJS International, LLC

Technodolly

CineTape

Tai Audio

Gamma Ray Digital Inc

Abel Cine

Glidecam

Paralinx LLC

The Slider

Wooden Camera