Negative Volume (1 Viewer)

[Andrew Pratt]

Granted there may be times where you can't get to reference from "0" but it hasn't happend to me yet in all the systems I've done. My Rotel processor uses a positive number scale so I do what you suggest in setting one channel equal to reference and ballence the others around it at that volume scale. For my system I just pick the 85 dB that Avia's SPL is set to and it seems to be close enough that I have no problems adjusting each channel to that level.

 

[ScottCHI]

i don't want to belabor a semantic point.

all i'm saying is that, unless a receiver has a feature to allow it to be re-zeroed once it's calibrated, the "0" on a receiver's volume scale doesn't represent anything.

 

[Kevin. W]

That's what I said I think we're just arriving at end point going in two different directions. I'm picking "0" on the dial and calibrating all the speakers to 75 or 85db by adjusting the trim of all the speakers. Your picking the position on the dial that gives you the same 75 or 85db level out off one speaker and then adjusting the others to match. Either way both off us as well as Andrew are saying "0" is irrelevant unless calibrated.

Kevin

 

[ScottCHI]

BUT, if you're using an autocalibrating receiver, it actually does pick a speaker to set to 75/85dB, THEN it resets the receiver's "0" point on the scale. THEN it adjusts the other individual speaker trims. so "0", in that case, is not irrelevant. it does represent reference volume.

 

[StephenL]

Why is 0 dB near the high end of the volume scale on some receivers and processors?

In digital recording, 0 dBFS (decibels full scale) is the peak level that can be recorded before digital clipping or overload occurs. Full scale is the level at which the binary number describing the signal is 1's in all places; it can't get any larger. All other measurements expressed in terms of dBFS will always be less than 0 dB (negative numbers). 0 dBFS is a logical reference for full scale because it can be used for any digital format regardless of the number of bits used to represent the signal. On some receivers and processors, the master volume level of 0 dB corresponds with the 0 dBFS level in Dolby Digital recordings.
http://www.jimprice.com/prosound/db.htm

If 0 dB is the maximum level before digital clipping or overload in a digital soundtrack, why does the master volume control go above 0 dB on some receivers and processors?

It's possible play back a digital soundtrack above the 0 dB reference level without clipping provided your amplifiers and speakers are capable. However, the dynamic range (the difference between the loudest peak and the softest level) will remain the same.

What is reference level?

Dolby or THX reference level is the volume level (sound pressure level) used in theaters for movie presentations (although this level is sometimes turned down). Digital formats are adjusted in the theater so that a digital signal level of -20 dBFS (20 dB below the 0 dB full scale level) will produce a sound pressure level of 85 dB at a distance two-thirds back in the theater. This allows a full-scale level of 105 dB per channel at the same distance.
http://www.audiovideo101.com/diction...-reference.asp
http://www.audiovideo101.com/diction...-reference.asp
http://www.jblpro.com/pub/cinema/cinedsgn.pdf

Some of the more sophisticated receivers and processors for home use (including those that are THX certified) provide individual speaker level calibration with the master volume at a designated, preset reference level corresponding with 0 dBFS. These receivers and processors automatically set the master volume to the reference level when the individual speaker levels are calibrated. This reference level is typically displayed as 0 dB on the master volume.

Why should speaker levels be calibrated relative to reference level?

Accurate calibration relative to 0 dBFS (the full-scale reference level) ensures that the sound pressure level produced by a sound system is the level intended by the sound engineer when the film's audio was mixed, regardless of whether the sound system is in a studio, commercial theater or home theater.

How loud is reference level?

Dolby Digital soundtracks have a dynamic range (the difference between the loudest peak and the softest level) of 105 dB for each channel. All recording levels are referenced to the 0 dBFS peak, so the minimum level in a Dolby Digital soundtrack is -105 dBFS. When a speaker receives a 0 dB full-scale signal from a Dolby Digital soundtrack, the sound pressure level should be 105 dB from each full-range channel and 115 dB from the Low-Frequency Effects channel. The ability to actually achieve the peak SPL in your home theater depends on the speakers, amplifiers and room.

If the 0 dB reference level corresponds with an SPL of 105 dB, isn't reference level too loud for normal listening?

Remember that 105 dB is the potential peak SPL at 0 dBFS (full-scale reference level). Dialog is typically well below the full-scale level. But many people find that the 0 dB reference level is too loud for most soundtracks. You can always reduce the master volume to provide a comfortable SPL.

What is dialog normalization?

The Dolby Digital recommended target level for dialog is -31 dBFS Leq(A), which is an output level 31 dB below 0 dB full-scale digital output, averaged over time using the equivalent loudness method. In order to maintain volume level consistency, Dolby Digital soundtracks contain a dialog level parameter (also known as dialogue normalization or dialnorm), which the decoder uses to automatically attenuate soundtracks that have a dialog level greater than -31 dBFS. The dialog level parameter is part of the soundtrack's metadata, which is data embedded in the digital audio data stream when the soundtrack is encoded. The scale used in the dialogue level setting ranges from -1 to -31 dB, in increments of 1 dB, where -31 dB represents no level shift. The Dolby Digital decoder adds the dialog level parameter to 31 dB to obtain the value of the level shift. For example, if a film has a dialogue level of -27 dBFS Leq(A), the sound engineer would include that dialog level parameter in the soundtrack's metadata. Your Dolby Digital decoder would add the -27 dB dialog level parameter to 31 dB resulting in a level shift of 4 dB. Your decoder would automatically reduce the volume by 4 dB. For dialog normalization to work as intended, the sound engineer must provide an accurate dialog level parameter in the metadata when the soundtrack is encoded.
http://www.hifi-writer.com/he/dictio...gnormalization
http://www.dolby.com/metadata/pa.st.0102.MDGuide.pdf
http://www.soundonsound.com/sos/dec0.../surround5.asp
http://www.hometheaterhifi.com/volum...on-6-2000.html
http://www.tweakers.net/nieuws/18061
http://www.globaldisc.com/Dolby/DDNorm.html
http://www.tvtechnology.com/features...12.10.03.shtml
http://etvcookbook.org/glossary/#D
http://etvcookbook.org/audio/dialnorm.html
http://www.smr-home-theatre.org/optimode/page3.html

How do I calibrate my home theater system at reference level?

Some receivers and processors (including those that are THX certified) have an internally generated test signal (pink noise) that is accurately calibrated relative to the 0 dB reference level. The internally generated pink noise in THX certified home equipment has a value of -30 dBFS. The Sound Pressure Level (SPL) that should correspond with the -30 dBFS test signal is 75 dB because the 0 dB full scale reference level corresponds with a peak SPL of 105 dB, and 105 dB - 30 dB = 75 dB. The user adjusts the individual speaker levels by observing a sound pressure level meter at the listening position so that each speaker produces 75 dBc (C-weighting, slow response) SPL with the internally generated pink noise and the master volume at the reference level of 0 dB.

Professional processors have a test signal with a value of -20 dBFS, so commercial surround sound systems are calibrated to 85 dBc SPL. Note that correctly calibrated home and professional systems will play identical soundtracks at the same SPL.
If your receiver or processor doesn’t have a designated point on the master volume scale that corresponds with the 0 dBFS reference level, and a test signal that is accurately calibrated relative to that level, you can use test signals from a DVD such as Avia or Video Essentials and note the level on the master volume that corresponds with the calibrated level. The most important objective when calibrating your receiver or processor is to make sure all speakers have the same output measure at the listening position.

How does room size, speaker sensitivity and speaker distance affect reference level?

Calibrating the individual speaker levels with the master volume at the 0 dB reference level eliminates variations due to speaker sensitivity, room size and distance between the listener and speakers. All systems that are properly calibrated at reference level will play the same soundtracks at the same SPL when the master volume is at 0 dB, provided the amplifiers have enough power and the speakers are capable of achieving the required SPL. There is no need to adjust the master volume to compensate for variations in speaker sensitivity and distance.

For example, consider the following two home theater systems:

The first is playing a Dolby Digital soundtrack at reference level (master volume at 0 dB) in a 2,000 cubic foot room with the listener 10 feet from speakers with relatively high sensitivity.

The second is playing the same Dolby Digital soundtrack at reference level (master volume at 0 dB) in a 4,000 cubic foot room with the listener 20 feet from speakers with relatively low sensitivity.

The two systems will produce the same SPL, provided both are properly calibrated, the amplifiers have enough power, and the speakers are capable of achieving the required SPL.
http://www.htguide.com/forum/archive/index.php4/t-2939


Related topics:
http://www.jimprice.com/prosound/db.htm

http://www.usa.denon.com/support/faqs_ht.asp#Q7

http://www.audiovideo101.com/diction...-reference.asp

http://www.hometheaterhifi.com/volum...on-6-2000.html

http://www.hometheaterhifi.com/volum...pril-2000.html

http://resmagonline.com/articles/pub...ticle_93.shtml

http://www.keohi.com/keohihdtv/exper.../avia_a2z.html

http://www.worldhistory.com/wiki/B/Bel.htm

http://www.free-definition.com/Bel.html

http://hometheaterhifi.com/forum/arc....php/t-61.html

 

[drobbins]

Stephen,
Thank you for your reply! It is very educational. Judging by the number of visits to this post, you have answered this question for many people.
Thanks,
Dave