Solved

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

Posted on 2001-09-11
7
1,658 Views
Last Modified: 2012-06-22
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
7 Comments
 
LVL 2

Expert Comment

by:udil
ID: 6475910
I'm not sure this is the right forum however, if
I'm not mistaken then 2DB means that the volume will be
3 time louder:
   10log2 = 3

And therefor if you perform a loop on N then the value
in DB will be:
  pow(10, (N/10))

However I don't think the volume is a function of the
distance raised to the power of 2 and in that case:
  pow(10, (pow(N, 2)/10))

If it wont work, try to ask a forum which is more
oriented to Physics or Electrical-Engineering people.
0
 
LVL 2

Expert Comment

by:bkdc
ID: 6476044
You should check out the following link (these guys are good):
http://music.calarts.edu/~glmrboy/musicdsp/music-dsp.html
0
 
LVL 3

Expert Comment

by:3rsrichard
ID: 6476550
And it's worse than you think;
At a simple level you just need to do a log conversion, ie.
if the user wants 1/2 volume lower it 6 dB, if he wants
1/4 volume thats 12 dB, 1/8 = 18 db, etc.

But, people don't hear quite that way, and if you have an
old style radio the volume control will be made so that
it uses a different scale ( called weighting).

You might develop a lookup table to translate from
"volume control position" to ::SetVolume
0
Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

 
LVL 1

Author Comment

by:mortonsw
ID: 6476803
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 1

Expert Comment

by:ua1zcl
ID: 6478166
Your question contain the following:
DSBVOLUME_MAX (no attenuation) =0
DSBVOLUME_MIN=-10000
DSBVOLUME_MAX - DSBVOLUME_MIN = 100 db

lpBuffObj->SetVolume( the argument from DSBVOLUME_MIN to DSBVOLUME_MAX);

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?

------------------------------------------------------------------
As i see, lpBuffObj->SetVolume( Volume - 10000) - is correct decision.
The decibell scale there represented as explanation and
additional calculation not reqired.
To get db scale simply devide by 100 value of Volume argument,
 Volume in db =Volume/100;

In Remarks section of SetVolume() function eplanation:
The volume is specified in hundredths of decibels (dB), i.e. lVolume in
 HRESULT SetVolume(LONG lVolume);
Alex
0
 
LVL 1

Author Comment

by:mortonsw
ID: 6480379
dB is logarithmic and I need linear. ramping setvolume with -10000 to 0 doesn't give me a linear fade. It gives me a logarithmic one. dividing the steps up doesn't change things.
0
 
LVL 2

Accepted Solution

by:
LoungeLizard earned 100 total points
ID: 6481279
for your function above, use:

DWORD ScaledVolume;

if(Volume <= 1)
  ScaledVolume = -10000;
else if(Volume > 10000)
  ScaledVolume = 0;
else
  ScaledVolume = log10(Volume)/4*10000 - 10000;

dsrval = lpBuffObj->SetVolume( ScaledVolume );


This should give you a percieved linear fade.
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

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

Often, when implementing a feature, you won't know how certain events should be handled at the point where they occur and you'd rather defer to the user of your function or class. For example, a XML parser will extract a tag from the source code, wh…
What is C++ STL?: STL stands for Standard Template Library and is a part of standard C++ libraries. It contains many useful data structures (containers) and algorithms, which can spare you a lot of the time. Today we will look at the STL Vector. …
The goal of the tutorial is to teach the user how to use functions in C++. The video will cover how to define functions, how to call functions and how to create functions prototypes. Microsoft Visual C++ 2010 Express will be used as a text editor an…
The viewer will learn additional member functions of the vector class. Specifically, the capacity and swap member functions will be introduced.

863 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

Need Help in Real-Time?

Connect with top rated Experts

20 Experts available now in Live!

Get 1:1 Help Now