Volume control and dB ?

Discussion in 'Archived Threads 2001-2004' started by Everett Painter, May 7, 2002.

  1. Everett Painter

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    Ok...I've had my Yamaha receiver for a couple of years now so I feel silly for asking this question. The volume knob has the following listings...at the bottom "-dB" and then as you turn up the volume the numbers go down....80, 40, 22, 20, 18 etc. How exactly do you read this? When someone talks about listening at 80dB, how do I find it on this dial? Thanks for the help.

    Everett
     
  2. John Garcia

    John Garcia Executive Producer

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    You need an SPL (Sound Pressure Level) meter to tell you at what point on your volume knob will give you the specified SPL. Using an SPL meter, you should calibrate each speaker individually, using your receiver's settings, to give you the same reading on the SPL meter. This will somewhat account for speaker location/distance from the listener, room effects, difference in speakers, etc... and should give you a more realistic sounding system.

    As for where that is on your dial, you will determine that by turning it to whatever level YOU consider to be LOUD. On my receiver that level is -8db, but I normally listen about -20 to -15, almost never at -8.
     
  3. Vince Maskeeper

    Vince Maskeeper Producer

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    Everett,
    This is a commonly misunderstood concept- so don't feel bad.
    The DB scale can measure many things-- specifically in the audio world- the decibel is used both to measure output sound pressure and internal signal level.
    To start with the output measure... the DB scale is used to measure Sound Pressure Level (SPL)- or how "loud" something is by the amount of air pressure it displaces. YOu might have seen the scale which shows a loud rock concert at 105db, and a Jet plane at 135...
    The person who mentioned listening at 80db is probably talking about output level of their system. However- as I'm sure you realize, sound pressure varies greatly throughout the course of a movie- so to say you listen at "80db" is a bit of a misnomer. What the person was probably referring to was the idea of Dolby Ref Level.
    Specifically- Dolby offers a specification that is known around these parts as Ref Level. Dolby ref level is basically a specific statement of maximum sound pressure output level for a dolby surround system. In the most simple expression: dolby has dictated an ideal target volume for listening to (or mixing) movies.
    This output level is "105db SPL output maximum from any single channel in the system (115 for LFE)". In other words- the loudest sound possible on the dolby soundtrack should come out of the speaker at 105db-- this also makes it so the dialog ends up being right about 75-80db spl of average peak volume.
    Usually you determine this level using test tones from discs like AVIA or Video Essentials along with a SPL meter to measure the output. These discs use test tones a specific number of steps below the maximum level- (For example- VE gives a tone 30 steps below max, so if you are listening dolby ref level it should measure 75db in SPL on your system... 105dbmax level minus 30db steps below= 75db).
    You play the test tone, and use a meter to measure it to a specific level (explained in the disc's on-screen instructions)- and you have just set your system for DOlby Ref level.
    HOwever, as a result- people mistakenly refer to the level of the test tones as their system level. For example they say they listen to something something at 75db or 85db, when these numbers are only meaningful when talking about the calibration discs. This is the source of much of the confusion, and much misinformation.
    Now, on your receiver- this db scale is referrig to internal levels. In the digital audio world-- the level of 0db is considered the MAXIMUM encoding level. All sound levels below max are labelled in negative values. So, you receiver's internal gain structure starts at -inf and goes up from there.
    How does this scale internal relate to the output scale in your case? Well, to be honest, it doesn't directly. The internal scale measures how much of the available audio signal is being sent to the amplifier stage in your receiver... but how much of that comes out and how loud you hear it are influenced by numerous factors such as amplifier wattage, speaker sensitivity, room size, speaker position, room acoustic properties, etc.
    The only way to make a determination of the ouput level of your system is to procure a test disc like AVIA or VE and test your system using a sound pressure meter. By doing so, you will be able to determine what internal db position on your receiver gives you a specific output level in your unique listening space.
    Hope that helps some
    Vince
     
  4. Everett Painter

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    Thanks guys! That was very helpful.

    Everett
     
  5. Wayne A. Pflughaupt

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