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From: wijesijp on 6 May 2010 12:47
>On May 6, 8:43=A0am, "wijesijp" <wijesena(a)n_o_s_p_a_m.gmail.com> wrote:
>> I am new to audio processing. What I wanted to do is amplify certain
>> frequencies in my data.
>>
>> I have written an application in c++ with a callback function that gets
t=
>he
>> audio data to a buffer. =A0Now I need to apply some function to this
data=
> to
>> amplify my frequencies.
>>
>> Can I do this using a filter?
>>
>> Is there an existing code I can use?
>>
>> Can someone point me in the right direction ?
>
>there are existing PROGRAMS that do this, i.e. audio editing programs
>called digital audio workstations (DAW).
>
>N-track studio for example allows you to basically draw the shape of
>the filter you would like and it will process a .wav file with that
>filter. You can even drag /change the filter shape while you listen
>to the playback in real time.
>
>Mark
>
>
>

I am developing this as an iPhone application. Is there some sample code or
free plug-in I can use?
From: Richard Dobson on 6 May 2010 14:43
On 06/05/2010 17:47, wijesijp wrote:
>
> I am developing this as an iPhone application. Is there some sample code or
> free plug-in I can use?

Try the musicdsp code archive:

http://www.musicdsp.org

I think it is pretty much understood that that code is in the public
domain (but note it is not necessarily uber-optimised; much will depend
on what you want to do). The filters are coded in floating-point; that
is OK on the iPhone (but double precision is probably fairly demanding
in CPU terms) so long as the final audio output is in the allowed format
- wither 16bit int or 8.24 fixed-point. Make sure that "Thumb" mode
(16bit arithmetic mode) is turned off in the compiler. If your filtering
is not more intense than, say, a simple multiband equaliser, you can
manage with 2nd-order filters (e.g. the RBJ set, very widely used in
both OS and commercial applications); but if you want the filters as
used in analog synths, you will need 3rd or 4th order filters (mood
emulations etc), which will tax the CPU that much more.

The previous advice to do some background reading is very well given.
For audio programming look for "Elements of Computer Music" by F.R.
Moore, which covers the basic theory of filters (and much else besides)
but has lots of code too. The "Csound Book" will also give you lots of
ideas, and Csound itself is a very good environment for trying out
processes before porting to the iPhone.

Richard Dobson

From: HardySpicer on 6 May 2010 15:08
On May 7, 12:43 am, "wijesijp" <wijesena(a)n_o_s_p_a_m.gmail.com> wrote:
> I am new to audio processing. What I wanted to do is amplify certain
> frequencies in my data.
>
> I have written an application in c++ with a callback function that gets the
> audio data to a buffer.  Now I need to apply some function to this data to
> amplify my frequencies.
>
> Can I do this using a filter?
>
> Is there an existing code I can use?
>
> Can someone point me in the right direction ?

Go and do an Elec End Major and find out...
Amateurs...

Hardy
From: Jerry Avins on 6 May 2010 23:21
On 5/6/2010 3:08 PM, HardySpicer wrote:

...

> Go and do an Elec End Major and find out...
> Amateurs...

Noah was an amateur. The Titanic and the Andrea Doria were built by
professionals.

Jerry
--
"I view the progress of science as ... the slow erosion of the tendency
to dichotomize." --Barbara Smuts, U. Mich.
�����������������������������������������������������������������������
From: Clay on 7 May 2010 10:34
On May 6, 11:21 pm, Jerry Avins <j...(a)ieee.org> wrote:
> On 5/6/2010 3:08 PM, HardySpicer wrote:
>
>    ...
>
> > Go and do an Elec End Major and find out...
> > Amateurs...
>
> Noah was an amateur. The Titanic and the Andrea Doria were built by
> professionals.
>

Well with the Titanic and the Andrea Doria, the main problem seems to
be not how they were built but how they were captained. They each ran
into a large object. You know that more scuba divers have died on the
wreck of the Andrea Doria than passengers died on the ship when it
sank? I've been on some deep wrecks but not that deep - it is too
dangerous.

Clay


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