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Re: lopsided tones.


As others have noted, there is some confusion on whether you added a DC offset or actually increased the positive portion of the waveform by deliberate distortion.

If you increased the positive portion of the waveform by intentional distortion,  then  the resultant waveform might be modeled as  sin( omega*t + theta) *  ( 1 +  0.3 * square wave of omega Hz*t, centered and sized so that the zero crossings match) .  In the frequency domain, the square wave modulation of the sine becomes a convolution of a  (theoretical) delta function  with a sinx/x function (sinc function), which is added to the original sine's delta function.  The additional terms in the harmonic spectrum should be that of a omega-frequency sinc function.  Of course, the finite-length signals will smear the spectrum.

You implied that your spectrum looked like a sine wave + DC, presumably on a log scale.  That would make me suspect that you did a DC offset and the flutter is from the loudspeaker, as others noted.



On Mon, Aug 17, 2009 at 12:41 PM, Ranjit Randhawa <rsran@xxxxxxxxxxx> wrote:
Dear List,
I have been experimenting with a 100hz tone, where the positive half sinusoid of the period is larger than the negative, the phase is however is not changed. Speech seems to have this profile of larger positive pulses as compared to the negative, hence my interest. Applying fft to such a signal, I get an increase in magnitude for the 100hz component, and an increase in the dc component. What I hear however is the basic 100hz tone, and a flutter on top of it, not what fft seems to indicate. My assumption was that the increased dc component would not be heard, and I would hear an increase in loudness of the 100 hz. However, the base 100hz loudness does not seem to change as I increase the area under the positive sinusoid, but the flutter does. Any history or explanation would be most welcome.
Thanks and regards,
Randy Randhawa