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Date Posted: 08:17:10 01/17/06 Tue
Author: OnM
Subject: DVD sound levels & whatnot
In reply to: LadyStarlight 's message, "Re: Off-Topic - has NBC found a loophole to annoy us with?" on 20:39:52 01/13/06 Fri

The short answer to this is that DVD's are capable of an extremely wide dynamic range, which is the distance between the softest and loudest parts. Measured in decibels (dB), this range can be over 100 dB. If you allow for things like explosions, thunder, jet engines etc to be at the top of the range, then normal conversation is about 40 to 50 dB below this, which is substantial. So, unless the dynamic range is compressed (squeezed into a smaller range, which some DVD players will actually do), the average sound level you hear seems very low compared to other sources, such as normal TV aound, VHS tapes, etc.

This is why DVD's sound best connected to a digital surround receiver and a good speaker system that can reproduce most of the available dynamic range, which the average TV speakers and amplifier simply cannot.

For comparison, here are approximate dynamic range figures for various audio media:

vinyl LP records - 30 to 60 dB
cassette tape w/o Dolby NR - 30 to 40 dB
cassette tape with Dolby NR - 40 to 50 dB
8-track tapes - 25 to 35 dB
open reel analog tapes (consumer) - 40 to 60 dB
open reel analog tapes (studio) - 50 to 70 dB
digital tape (DAT) - 90 to 95 dB
digital studio recorders, 24 bit - 120 to 140 dB
normal TV broadcast audio (analog) - 30 to 40 dB
VHS videocassette (linear mono track) - 20 to 30 dB
VHS videocassette (HiFi tracks) - 40 to 60 dB
Laser videodisc (analog tracks) - 50 to 60 dB
Laser videodisc (digital tracks) - 80 to 95 dB
DVD discs - 90 to 140 dB
HD-DVD & Blu-Ray discs (likely) - same as DVD

In sound pressure level terms (dB/SPL), 0 db is the softest sound the human ear can detect. 120 dB is the threshold of pain (physical overload of the ear internals itself). Each change of 10 dB is a ten-fold difference in acoustic power. Thus, 60 db is 1 million times more acoustic power than 0dB. You can do the math for the rest.

Our ears are amazing things!

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