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Subject: Re: Optimum Audio Levels
From: BlueChip (cs_bluechip_at_webtribe.net)
Date: 2004-06-03


At 20:05 03/06/04, you wrote:
>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 would have guessed that a sine wave form at 1KHz would probably be the
most appropriate choice - but I am reaching the end of my knowledge and
moving gently into speculation now.

>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
>>
>>
>>
>>
>>--
>>Incoming mail is certified Virus Free.
>>Checked by AVG Anti-Virus (http://www.grisoft.com).
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>
>
>Stuart Engelke
>WMCA WWDJ NY
>201-298-2108
>
>_______________________________________________
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