As Neven pointed out, the LOG is base 10, not a natural log (which is base e), so
P1/P2 = 10^(db/10) and 10^(-3/10) = 0.5 ----- Original Message ----- From: "Ross Levis" <[EMAIL PROTECTED]> To: "Multiple recipients of list delphi" <[EMAIL PROTECTED]> Sent: Thursday, 6 March 2003 16:54 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. > > > > > > > > -------------------------------------------------------------------- ------- > > > New Zealand Delphi Users group - Delphi List - > > [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> > > > Website: http://www.delphi.org.nz > > > To UnSub, send email to: [EMAIL PROTECTED] > > <mailto:[EMAIL PROTECTED]> > > > with body of "unsubscribe delphi" > > > Web Archive at: http://www.mail-archive.com/delphi%40delphi.org.nz/ > > > > > > > -------------------------------------------------------------------- ------- > New Zealand Delphi Users group - Delphi List - [EMAIL PROTECTED] > Website: http://www.delphi.org.nz > To UnSub, send email to: [EMAIL PROTECTED] > with body of "unsubscribe delphi" > Web Archive at: http://www.mail-archive.com/delphi%40delphi.org.nz/ --------------------------------------------------------------------------- New Zealand Delphi Users group - Delphi List - [EMAIL PROTECTED] Website: http://www.delphi.org.nz To UnSub, send email to: [EMAIL PROTECTED] with body of "unsubscribe delphi" Web Archive at: http://www.mail-archive.com/delphi%40delphi.org.nz/
