Right,... "deca" would be going the other way, and not "deci".
Knew thee was something about that I was forgetting. Thanks.

-Partev


=================================================================

--- vip@avatar.com.au wrote:

From: DavidW 
To: csound@lists.bath.ac.uk
Subject: [Csnd] Re: Re: dynamic range
Date: Sat, 14 Feb 2009 12:05:01 +1100

Just for the record ....
A decibel is 1/10 of a bel not the other way around.
And the reason its a logarithmic scale is has little to do with the  
size of graph paper -
it's because changes in the physical phnomenon called amplitude, is  
heard as the psychophysical phenomenon called  loudness, and the  
relationship between them is logarithmic. i.e we hear logarithmically.

for a simple intro, see: http://www.avatar.com.au/courses/PPofM/intensity/Intensity1.html

D.

On 14/02/2009, at 10:36 AM, Partev Barr Sarkissian wrote:

> I think I see what Victor is saying,
> dB is a relative relationship power ratio between two power levels.
>
> I was taught that it is a "log" scale, because the linear scale
> version of that was too difficult to graph, so logrithmic graphing
> was used so it would all fit on the graph paper used back then.
> A Bel is a small increment based on a given power level ratio.
> A Deci-Bel required a huge graph paper to graph it, too cumbersome,
> so a logrithmic scale was used to better graph it.
> That's the history as I recall it (please correct as needed).
>
> It's applicable to Volts, Watts, gain and as well as acoustical SPL
> and pretty much any other powers ratio if memory serves. It's a power
> level relationship relative to another power level.
>
> So, Victor, that about sum it up?  BTW: Saw the correction in the
> December issue of JAES regarding that Taylor Series problem.  :-)
>
> -Partev
>
>
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> ======================================================================
>
>
>
>
> --- richarddobson@blueyonder.co.uk wrote:
>
> From: Richard Dobson 
> To: csound@lists.bath.ac.uk
> Subject: [Csnd] Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re:  
> dynamic range
> Date: Wed, 07 Jan 2009 10:11:55 +0000
>
> victor wrote:
>> Again, I don't agree, I'm sorry. Ampdb() does not express
>> amplitudes in any system, as far as I can see, but just converts
>> a ratio into the SPL scale (which is expressed as 20log10(ratio)).
>> This can be applied to any input.
>>
>
>
> It's simply a matter of the range, and the reference value.
>
> 20. *  log10(32767) ~= 90.3
>
> Except that  "by convention" 32767 was defined as Csound's maximum
> positive value before clipping; i.e. it posits a 16bit sample range
> (which is why some people still seem to thiunk Csound is somehow a  
> 16bit
> system).  Whereas the global audio industry standard is to define that
> as 0dBFS. If we therefor want to express a level in industry terms of
> -6dB,  we know that would be 16384;  but the formula above gives it as
> 84.2.  That is how the usage was defined in the original manual.
>
> Hence  the ampdbfs pair, to express all levels relative to digital  
> peak
> = 0dBFS. And subsequently the 0dbfs opcode itself, intended finally to
> render the old 16bit representation obsolete and (ideally) deprecated.
> The mathematics is not in question; the choice of reference level is.
> The new opcodes  simply enabled Csound to express itself in a way
> exactly compatible with industry practice.
>
> Richard Dobson
>



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