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Subject: Re: dB volume
From: BlueChip (cs_bluechip_at_webtribe.net)
Date: 2004-03-19


>>I would also prefer a dB display going from -something dB to 0dB.
>
>So are you recommending that Rockbox report the +12dB point as 0dB? Or
>did you want Rockbox changed so that the highest value of 0dB is what we
>call 93% now?

These are all the same:
# Archos 100%
# Rockbox 92%
# MAS 0dB

Archos puts the max vol at "0dB" so that digital distortion is not a risk.

Rockbox puts the max vol at "12dB" so that quiet tracks/poor recordings can
be cranked up to an audible level.

>I'm confused about all of this. A decibel is a logarithmic expression of
>the ratio between two signal power, voltage, or current levels. Assuming
>that P2 and P1 are power in watts, the decibel rating can be calculated as:
>
>dB = 10 log10 (P2 / P1)
>
>I understand that the wattage can be measured at the headphone output, but
>how is it measured internally?
>
>Note: Decibels can be calculated in terms of the effective voltage if the
>load impedance remains constant: dB = 20 log10 (V2 / V1). Since the
>headphones vary wildly in impedence, that calculation is out the window.
>
> > I don't think this is so unusual - all the modern amplifiers /
> > receivers (including mine) show volume in dB.
>
>While typical mid-fi consumer products do that, high-end audio components
>and professional products generally do not:
>
>http://www.adcom.com/preamplifiers/gfp750.htm
>http://www.atma-sphere.com/products/mp3.html
>http://www.legendaudio.com/prod02.htm
>http://www.ys-audio.com/symphonies.htm
>www.metaxas.com/pages/products/ opulence.html
>http://www.tascam.com/images/popups/TASCAM_AV452Front_Rear.jpg
>
>Regards,
> Fred Maxwell
>
>_______________________________________________
>http://cool.haxx.se/mailman/listinfo/rockbox

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