Re: [DUG]: db calculation

Wed, 05 Mar 2003 23:49:29 -0800

This gives me roughly 0.2511, not 0.5 with -3db

Cheers,
Ross.

Neven MacEwan wrote:

Ross

exp() is a natural log, ie exponential of e,  not exponential of 10
Delphi has a log10 function but no Exp10 function I can see so
To do this you do use

exp(db/10*ln(10))

HTH

Neven
----- Original Message -----
From: "Ross Levis" <[EMAIL PROTECTED]>
To: "Multiple recipients of list delphi" <[EMAIL PROTECTED]>
Sent: Thursday, March 06, 2003 4:54 PM
Subject: Re: [DUG]: db calculation




Hi

This formula doesn't seem to work.  The 20 should be 10 as Neven pointed
out but I believe a -3db reduction should take 65535 to 32767 but it's
not close.  Any ideas?

Cheers,
Ross.

Nello Sestini wrote:



        (db/20)
P1 = P2  e

i.e. P1 = P2*exp(db/20)


not sure if this is what you are after
(and hope i haven't made some stupid mistake)



-ns
http://www.roserox.co.th


----- Original Message -----
From: "Ross Levis" <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>>
To: "Multiple recipients of list delphi" <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>>
Sent: Thursday, March 06, 2003 09:57
Subject: [DUG]: db calculation



Here's a maths question for you.  I've never been that good at maths,
particularly logarithms

Does anyone know the formula to alter an integer value by a particular
db value.

I'm working on an audio app and I need to alter the volume by a
particular db setting.  The volume can be anywhere in the range 0
(silent) to 65535 (maximum).

I know that db = 20 log (P1/P2) though I've also seen the 20 at 10.


How


do I get P1 (or is it P2) to the left of the equation.

Thanks,
Ross Levis.




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