Solved

Need equation for converting decibels (dB) to standard scale 0 to 10000

Posted on 2001-09-11
5
312 Views
Last Modified: 2013-12-03
I need to fade volume of a DirectSound buffer but IDirectSoundBuffer:SetVolume wants the volume level specified in in hundredths of decibels (dB). Allowable values are between DSBVOLUME_MAX (no attenuation) and DSBVOLUME_MIN (silence). These values are currently defined in Dsound.h as 0 and -10,000 respectively. The value DSBVOLUME_MAX represents the original, unadjusted volume of the stream. The value DSBVOLUME_MIN indicates an audio volume attenuated by 100 dB, which, for all practical purposes, is silence.

Ramping SetVolume between -10000 and 0 (to fade in) results in a audibility between about -4000 and 0 and gives me a quick fade at the end of my ramp. I need a steady fade throughough. How do I convert say 0 to 10000 to necessary SetVolume argument that gives me a steady ramp? Thanks!!

I found two leads that may help but unsure how to translate into c:

http://picard.coma.sbg.ac.at/coma/docu/AF/docs/man3/AFdBtoLin.html

http://picard.coma.sbg.ac.at/coma/docu/AF/docs/man3/AFLintodB.html
0
Comment
Question by:mortonsw
  • 3
  • 2
5 Comments
 
LVL 5

Expert Comment

by:robpitt
ID: 6476532
Decibels are logarithmic scale - see http://www.phys.unsw.edu.au/music/dB.html

Anyway try something like:-

    db = 10 * log10( percent/100 );
0
 
LVL 5

Expert Comment

by:robpitt
ID: 6476719
and inversely:
  percent = 100 * pow(10,db/10);
0
 
LVL 1

Author Comment

by:mortonsw
ID: 6476800
I know very little C (I write in ASM and interface) but my func to call DirectX SetVolume is in C and accepts arg (0 to 10000) which it subtracts 10000 from in order to pass to SetVolume (since it wants -10000 to 0).

extern "C" BOOL FAR PASCAL DXSBSetVolume( LPDIRECTSOUNDBUFFER lpBuffObj , DWORD Volume)
{
    dsrval = lpBuffObj->SetVolume( Volume-10000 );
    if(dsrval == DS_OK) return TRUE;  
    return FALSE;
}

What's the necessary code to use to handle calling argument as 100ths of percent (ie, 10000 = 100.00%), convert to decibel scale and pass to SetVolume as -10000 to 0?
0
 
LVL 5

Accepted Solution

by:
robpitt earned 100 total points
ID: 6477934
Given an 'inputVolume' measured in hundredths of a percent,
i.e. from 0 (silence) to 10000 (max), try the following:

MySetVolume( DWORD inputVolume)
{
    double decibels;
    DWORD dsVol;

    if (inputVolume==0)
        dsVol = DSBVOLUME_MIN;
    else if (inputVolume>10000)
        dsVol = DSBVOLUME_MAX;
    else
    {
        //convert linear inputVolume to decibels (logarithmic)
        decibels = 10.0 * log10((double)inputVolume / 10000.0);
        dsVol = (DWORD)(decibels * 100.0);
    }

    pDSBuffer->SetVolume( dsVol );
}


...think thats right.
0
 
LVL 1

Author Comment

by:mortonsw
ID: 6478022
20.0 * log10(... worked perfectly. Thanks!!
0

Featured Post

Master Your Team's Linux and Cloud Stack

Come see why top tech companies like Mailchimp and Media Temple use Linux Academy to build their employee training programs.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Fix insertion and shifting issue 5 62
Insert filename column as column a 18 76
Example of WebAPI 7 33
How to copy an image file into clipboard C/C++? 1 171
This article shows a few slightly more advanced techniques for Windows 7 gadget programming, including how to save and restore user settings for your gadget and how to populate the "details" panel that is displayed in the Windows 7 gadget gallery.  …
This article shows how to make a Windows 7 gadget that extends its U/I with a flyout panel -- a window that pops out next to the gadget.  The example gadget shows several additional techniques:  How to automatically resize a gadget or flyout panel t…
This tutorial gives a high-level tour of the interface of Marketo (a marketing automation tool to help businesses track and engage prospective customers and drive them to purchase). You will see the main areas including Marketing Activities, Design …
This is Part 3 in a 3-part series on Experts Exchange to discuss error handling in VBA code written for Excel. Part 1 of this series discussed basic error handling code using VBA. http://www.experts-exchange.com/videos/1478/Excel-Error-Handlin…

803 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question