Re: [music-dsp] Sinewave generation - strange spectrum

Rob Belcham Tue, 26 Apr 2011 13:38:37 -0700

If it's possible to record the time-domain audio output & plot it, thatmight help in trying to figure out where the problem is.


Is the audio clipping perhaps, what is the amplitude set to ?

Have you tried copying the input buffer directly to the output buffer so youcan rule out everything except your algorithm ?


Regards
Rob

-----Original Message-----From: Alan Wolfe

Sent: Tuesday, April 26, 2011 9:14 PM
To: A discussion list for music-related DSP
Subject: Re: [music-dsp] Sinewave generation - strange spectrum

just stabbing in the dark in case nobody else gives a more useful
response but...

#1 - what is the format of your output?  If it's low in bitcount that
could make the signal more dirty i believe (less resolution to make a
more perfect sine wave)

#2 - have you tried calculating via doubles?

#3 - what is data->amplitude... does that ever change or is it just a
one time set volume adjustment for the left and right channels?

On Tue, Apr 26, 2011 at 12:57 PM,  <eu...@lavabit.com> wrote:

Hello,

I want to generate two different frequency sinewaves on LineOut -
Left&Right. For audio IO I'm using Portaudio(Linux, PortAudio V19-devel
(built Apr 17 2011 22:00:29)), and the callback code is:

static int paCallback( const void* inBuff, void* outBuff,
                                               unsigned long frpBuff,

constPaStreamCallbackTimeInfo* tInf,PaStreamCallbackFlagsflags,

                                               void* userData )
{
       int16_t i;
       audioData* data = (audioData*) userData;
       float* out = (float*) outBuff;

       /* Prevent warnings */
       (void) tInf;
       (void) flags;

       for( i=0; i<frpBuff; i++ )
       {

*out++ = data->amplitude[0] * sinf( (2.0f * M_PI) *data->phase[0] );*out++ = data->amplitude[1] * sinf( (2.0f * M_PI) *data->phase[1] );


               /* Update phase, rollover at 1.0 */
               data->phase[0] += (data->frequency[0] / SAMPLE_RATE);
               if(data->phase[0] > 1.0f) data->phase[0] -= 2.0f;
               data->phase[1] += (data->frequency[1] / SAMPLE_RATE);
               if(data->phase[1] > 1.0f) data->phase[1] -= 2.0f;
       }

       return paContinue;
}

When I checked the output spectrum for a 10kHz frequency using baudline
(running on another PC), I got this http://images.cjb.net/80af2.png . The
spectrum is clean only for output frequencies below 2-3 kHz.

The tone generator inside baudline gives a clean spectrum at 10 kHz:
http://images.cjb.net/b943b.png .

What method would you recommend for generating a clean sinewave at 5-12kHz?

I think there is a bug somewhere, because the sine is computed in float
for each sample and should be precise enough...

Thanks



--
dupswapdrop -- the music-dsp mailing list and website:

subscription info, FAQ, source code archive, list archive, book reviews,dsp links

http://music.columbia.edu/cmc/music-dsp
http://music.columbia.edu/mailman/listinfo/music-dsp

--
dupswapdrop -- the music-dsp mailing list and website:

subscription info, FAQ, source code archive, list archive, book reviews, dsplinks

http://music.columbia.edu/cmc/music-dsp

http://music.columbia.edu/mailman/listinfo/music-dsp

--
dupswapdrop -- the music-dsp mailing list and website:
subscription info, FAQ, source code archive, list archive, book reviews, dsp 
links
http://music.columbia.edu/cmc/music-dsp
http://music.columbia.edu/mailman/listinfo/music-dsp

Re: [music-dsp] Sinewave generation - strange spectrum

Reply via email to