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Subject: Re: Optimum Audio Levels
From: Stu Engelke (engineer_at_nycradio.com)
Date: 2004-06-03


The next question that arises is what is considered a "normal" level for
recording an mp3 file.
Around here we use about 18dB below full scale. That is, if a wav file were
to be recorded until it ran out of bits the '0' level would be 18dB below
that. That would give 18 dB of headroom to avoid clipping. Some use -24.

I have test equipment that can measure the output of the Archos V2 on a
scope or with an audio precision test set. I just need some "standard"
test file. I can make a file with Audacity.

I guess that making a file with Audacity recorded at as close to 100% as
possible and measuring that would be a place to start.

I'll try to do that and post the results.

Stu

At 07:17 PM 6/3/2004 +0100, you wrote:

>>Some definition of 0dB and +12 and _ 60 is necessary. dB by its
>>definition is a relative scale. 0 is usually what we are referring
>>everything else to. The last letter in dBv dBu dBm etc gives a clue.
>>
>>So if you use dBv 0dB is 1 volt coming out of the headphone jack. dBm
>>would be around .7 V
>>
>>That is what is so nice about standards. There are so many to choose from.
>>Stu
>
>Yes, dB ...what a totally useless term.
>
>Sadly I have a hoard of Micronas documentation and don't recall reading
>anything that gives any more information about this than that found on
>page 45 of the Datasheet which can be found on the Rockbox docs page.
>
>I don't recall which doc contained the gem that "0dB" produced "Line Level
>Output", but as it concurred with two real life tests it seems acedemic really.
>
>I believe the last test was performed by comparing the output of the
>jukebox with that of the "line level output of my car cd player"
>...perhaps this guy (steve was it?) could offer something more helpful.
>
>My guess is dBv, as I understand the most common definition of Line Level
>to be "1V peak to peak".
>
>You seem to be quite knowledgeable ...do you own or have access to a scope?
>
>As for the reference sound level - I'm guessing that'll be some internal
>DAC thing.
>
>For now, I am content to ride with the official MAS docs ...but if they
>are wrong, and it wouldn't surprise me, then we can tweak the code quickly
>enough.
>
>> > ============================================
>> > What is the VOLUME range you use most often?
>> > ============================================
>>
>>Sorry to chime in late -- just catching up today. I use:
>>
>>55 - 62 with headphones in bed at night
>>72 - 75 with headphones during the day when it's fairly quiet around
>>82+ when it's noisy around, and in the car through cassette adapter.
>>
>>Hope this helps!
>>Leslie
>
>Added - thanks ;)
>...More good news :)
>
>>Sorry to contribute late. Headphones as low as 45% when going to sleep. (I
>>couldn't use the original Archos at all for this purpose because the volume
>>didn't go low enough!!).
>>Matt
>
>I've added your vote to the graph as 45..54
>
>Rockbox 45% = 127*45/100 = 57MAS -58dB
>
>The algorithm I've settled on goes down to -61dB with accuracy, so
>...<phew> ;)
>
>I'm amazed that the original Archos scale only ran from Rockbox 50%...92%
>- there aren't 100 discreet steps between those numbers - LOL
>
>Thanks all,
>
>BlueChip
>_______________________________________________
>http://cool.haxx.se/mailman/listinfo/rockbox
>
>
>
>
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Stuart Engelke
WMCA WWDJ NY
201-298-2108

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