Playing a sine wave

Playing a sine wave

[Hrafnkell Eiriksson]

Hi

Is it possible to use the sequencer stuff in the OSS sound driver
to let the sound card play a sine wave of a given frequency?
Any pointers to info on how to do that if it is possible?

-- 
//-----------------------//-------------------------------------------------
//  Hrafnkell Eiriksson  //  Student of Computer- and Electrical engineering
//  hkelle@rhi.hi.is     //  at the Univeristy of Iceland
//                       //  "Blessed are they who go around in circles,
//  Finger for PGP key   //   for they shall be known as Wheels"

Re: Playing a sine wave

[Hannu Savolainen]

On Wed, 12 May 1999, Hrafnkell Eiriksson wrote:

> Hi
> 
> Is it possible to use the sequencer stuff in the OSS sound driver
> to let the sound card play a sine wave of a given frequency?
In theory it's possible to play sine waves using the OPL3 FM synth chip
available on most older (ISA) soundcards. However this is very inpractical
way.

A much easier way is using /dev/dsp. You only need to construct few cycles
of sine wave at given frequency to a buffer. Then just keep writing this
buffer to /dev/dsp as many times as you need. In fact it may even be
possible that somebody has already written this kind of app (look at
ftp://sunsite.unc.edu/pub/Linux/apps/sound).

Best regards,

Hannu
-----
Hannu Savolainen (hannu@opensound.com)
http://www.opensound.com (Open Sound System (OSS))
http://www.compusonic.fi (Finnish OSS pages)

Re: Playing a sine wave

[Eric Mitchell]

Hannu Savolainen wrote:
> 
> On Wed, 12 May 1999, Hrafnkell Eiriksson wrote:
> 
> > Hi
> >
> > Is it possible to use the sequencer stuff in the OSS sound driver
> > to let the sound card play a sine wave of a given frequency?
> In theory it's possible to play sine waves using the OPL3 FM synth chip
> available on most older (ISA) soundcards. However this is very inpractical
> way.
> 
> A much easier way is using /dev/dsp. You only need to construct few cycles
> of sine wave at given frequency to a buffer. Then just keep writing this
> buffer to /dev/dsp as many times as you need. In fact it may even be
> possible that somebody has already written this kind of app (look at
> ftp://sunsite.unc.edu/pub/Linux/apps/sound).

The source for esound (http://www.tux.org/~ricdude/EsounD.html)
includes the code necessary to do this in the file, esd.c.  I have
reproduced it below for your convenience:

Feel free to ask if you have any questions on the code.

buf is the buffer to store the audio data in,
format determines whether to use 8bit unsigned or 16bit signed data,
magl is the magnitude for the left side,
magr is the magnitude for the right side,
freq is the desired frequency in Hertz,
speed is the playback rate of the audio device,
length is the number of samples to be stored in buf,
offset is used to get a perfect sine waves, buffer after buffer,
    by setting offset to the product of the number of buffers already 
    played and the length of the buffer in samples.


void set_audio_buffer( void *buf, esd_format_t format,
		       int magl, int magr, 
		       int freq, int speed, int length, long offset )
{
    int i;
    float sample;
    float kf = 2.0 * 3.14 * (float)freq / (float)speed;

    unsigned char *uc_buf = (unsigned char *)buf;
    signed short *ss_buf = (signed short *)buf;
    
    /* printf( "fmt=%d, ml=%d, mr=%d, freq=%d, speed=%d, len=%ld\n",
       format, magl, magr, freq, speed, length ); */

    switch ( format & ESD_MASK_BITS )
    {
    case ESD_BITS8:
	for ( i = 0 ; i < length ; i+=2 ) {
	    sample = sin( (float)(i+offset) * kf );
	    uc_buf[i] = 127 + magl * sample;
	    uc_buf[i+1] = 127 + magr * sample;
	}
	break;
    case ESD_BITS16:	/* assume same endian */
	for ( i = 0 ; i < length ; i+=2 ) {
	    sample = sin( (float)(i+offset) * kf );
	    ss_buf[i] = magl * sample;
	    ss_buf[i+1] = magr * sample;
	}
	break;
    default:
	fprintf( stderr, 
		 "unsupported format for set_audio_buffer: 0x%08x\n", 
		 format );
	exit( 1 );
    }


    return;
}


> Best regards,
> 
> Hannu
> -----
> Hannu Savolainen (hannu@opensound.com)
> http://www.opensound.com (Open Sound System (OSS))
> http://www.compusonic.fi (Finnish OSS pages)

-- 
+=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=+
| Eric B. Mitchell         mailto:emitchell@altaira.com |
| tel: (301) 809 - 3534    Altair Aerospace Corporation |
| tel: (800) 7 - ALTAIR    4201 Northview Dr. Suite 410 |
| fax: (301) 805 - 8122    Bowie, MD  20716             |
+=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=+
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         |   //  \  ||    ||   //  \  || ||__/
         |  //--=\ |L--/ ||  //--=\ || || "=,
          \      ---==/
           \____---==/

Re: Playing a sine wave

[Itai Nahshon]

>> Is it possible to use the sequencer stuff in the OSS sound driver
>> to let the sound card play a sine wave of a given frequency?
>In theory it's possible to play sine waves using the OPL3 FM synth chip
>available on most older (ISA) soundcards. However this is very inpractical
>way.
>
>A much easier way is using /dev/dsp. You only need to construct few cycles
>of sine wave at given frequency to a buffer. Then just keep writing this
>buffer to /dev/dsp as many times as you need. In fact it may even be
>possible that somebody has already written this kind of app (look at
>ftp://sunsite.unc.edu/pub/Linux/apps/sound).

See
   http://metalab.unc.edu/pub/Linux/apps/sound/dtmf-dial-0.2.tar.gz   

It combines two sine waves and outputs to /dev/dsp. You are
welcome to hack on it. Internally it has the function to
produce sine waves at any integer frequency and sampling rate.

Itai

Re: Playing a sine wave

[Cornelius Creedon]

hm. there is a package called siggen to do such things, dont know which
devices it uses though...

-cc

On Wed, 12 May 1999, Hrafnkell Eiriksson wrote:

> Hi
> 
> Is it possible to use the sequencer stuff in the OSS sound driver
> to let the sound card play a sine wave of a given frequency?
> Any pointers to info on how to do that if it is possible?
> 
> -- 
> //-----------------------//-------------------------------------------------
> //  Hrafnkell Eiriksson  //  Student of Computer- and Electrical engineering
> //  hkelle@rhi.hi.is     //  at the Univeristy of Iceland
> //                       //  "Blessed are they who go around in circles,
> //  Finger for PGP key   //   for they shall be known as Wheels"
> 

Re: Playing a sine wave

[Jeff Tranter]

On Wed, 12 May 1999, Hannu Savolainen wrote:

> A much easier way is using /dev/dsp. You only need to construct few cycles
> of sine wave at given frequency to a buffer. Then just keep writing this
> buffer to /dev/dsp as many times as you need. In fact it may even be
> possible that somebody has already written this kind of app (look at
> ftp://sunsite.unc.edu/pub/Linux/apps/sound).

Yes, I wrote such a program using /dev/dsp. Look for "wave"
on sunsite.unc.edu, probably in the directory mentioned above
unless they moved it.

It can do sine, square, triangle, and ramp waveforms, in stereo.

--
Jeff Tranter (mailto:tranter@pobox.com http://www.pobox.com/~tranter)
Currently running Linux 2.2.7      Learn more at http://www.linux.org

Re: Playing a sine wave

[Hrafnkell Eiriksson]

On 12. May 1999, Hannu Savolainen wrote:
> A much easier way is using /dev/dsp. You only need to construct few cycles
> of sine wave at given frequency to a buffer. Then just keep writing this
> buffer to /dev/dsp as many times as you need. In fact it may even be
> possible that somebody has already written this kind of app (look at
> ftp://sunsite.unc.edu/pub/Linux/apps/sound).

What about creating a patch with the sine wave and use the
wavetable stuff to play it. Thay way the wavetable could
change the playback frequency etc.
(Please note that I hardly know what a wavetable is nor what
it can do :) 

-- 
//-----------------------//-------------------------------------------------
//  Hrafnkell Eiriksson  //  Student of Computer- and Electrical engineering
//  hkelle@rhi.hi.is     //  at the Univeristy of Iceland
//                       //  "Blessed are they who go around in circles,
//  Finger for PGP key   //   for they shall be known as Wheels"