Re: Waveform horror! Is a 44.1 kHz sampling rate sufficient?


"Michael" <mrdarrett@xxxxxxxxx> wrote in message
news:609e9c8b-ca5e-4718-bf0e-f3730c6536f1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I used Audacity to generate a 19 kHz tone, planning on burning it to a
CD and playing it in my car stereo for... um... well, let's not get
into that. I then zoomed in on the waveform to take a peek, prior to
burning the waveform. What horror!

http://mrdarrett.googlepages.com/distort.jpg

The waveform is severely distorted. I could see where the points
mathematically
would be correct, but given the sparse sampling points, the speaker
would not be instructed to swing rail-to-rail at, say, between 15.0000
and 15.0005 seconds.

A FFT gives a spread of frequencies centered around the 19 kHz, but,
yuck!

I tried various other frequencies: 9 kHz gives a pretty distorted
waveform as well.

What are the implications as far as accurate sound reproduction at a
44.1 kHz
sampling frequency, as used by CDs?

Michael

The points you are seeing that look distorted is because of the sparse
sampling and it is not a divisor of 44.1khz. The spline representation is
simply not going to show a perfect sine wave. If you were to try to fit a
sine wave to that data you would find it would fit really well. But because
the peaks are not sampled in some cases it looks like something entirely
different(related to aliasing).

The data though is still a sine wave and will sound like one. The fourier
transform(the spectrum) of any pure signal is not pure and will always be a
"mash" of frequencies around the center frequency(this is because of
numerical errors in the calculations).

I wouldn't worry about it. If you get a better program that uses a better
interpolation method then it won't look bad.


.

Relevant Pages

  • Re: MSP430F1612: generating sinusoidal signals
    ... Code uses the fewest cycles to implement periodic waveform with DACs. ... a 32 kHz sample and interrupt rate. ... For audio applications just over 2-3 times the highest sine wave ... other phase accumulator sizes and look-up table sizes can ...
    (comp.arch.embedded)
  • Re: Anti Aliasing of Arbitrary Waveforms
    ... And it applies to any periodic waveform. ... on the phase of the sampler relative to the generator. ... every 10 samples and at 19 KHz signal will repeat at something like every 190 ... So the 19KHz signal will have a whole bunch of frequencies that aren't ...
    (comp.dsp)
  • Re: Waveform horror! Is a 44.1 kHz sampling rate sufficient?
    ... I then zoomed in on the waveform to take a peek, ... A FFT gives a spread of frequencies centered around the 19 kHz, but, ... and the DAC is followed by a lowpass filter. ...
    (sci.electronics.basics)
  • Re: Anti Aliasing of Arbitrary Waveforms
    ... And it applies to any periodic waveform. ... every 10 samples and at 19 KHz signal will repeat at something like every 190 ... So the 19KHz signal will have a whole bunch of frequencies that aren't ... 200 KHz sample rate that will produce a 20 kHz tone. ...
    (comp.dsp)
  • Re: Function Generator Agilent 33220A Arbitrary Waveform using Matlab
    ... The full 6 seconds will consists of one cycle of my ... waveform, then later I would be able to repeat it (for around 10 ... a cycle would exceeds he 64K points limitation in Agilent 33220A. ... cycle in a different way (of course without altering the frequencies). ...
    (comp.soft-sys.matlab)