It would be interesting to hear from Jon more about his application and
what he intends to sample.  My interest was simply in developing an
algorithm that gave evenly spaced samples at the highest resolution
possible for the period concerned, without any special data logger setup.
"Evenly spaced" because that was difficult to do but also because it
simplifies subsequent analysis (I am talking here about environment
variables). Andrew & Jennifer show a method where this requirement is
relaxed.

Ron

On Thu, 6 Nov 1997, Wayne Foletta wrote:

> Hi Data Logger Coders:
>
> I've been following the thread on the 60 sample evenly spaced - but my
> question is "Why evenly spaced samples?". What's the basic reason for
> sampling in this manner? If the intent is reconstruct a signal waveform,
> changing the sample interval by Nyquist theory will reduce the
> reconstructed waveform bandwidth directly with the increased time
> between samples. So what is the importance of even samples? Have I
> missed a post on the basics? Who or what is the signal observer and what
> is the signal source?
>
> Mike Keitz is right on the fundamentals of simple resampling - linear
> interpolation does work. You only need to use more complex DSP routines
> if you want to account for sampling aperture (sinc 1/fs rolloff) and
> sample resolution. If the human eye is the observer, 8 bits and linear
> resampling is transparent. However, if it is the human ear, 8 bits and
> linear resampling sounds good only if the original signal is oversampled
> by a factor 10 or more (CD playback chips use 16x or more with 6+ order
> elliptic DSP filters for 16 bit Hi Fi).
>
> PS: The term 'warping' when applied to voice or other sampled signals
> usually refers to changing the time or pace of the signal without a
> frequency shift or pitch change.
>
> -Wayne
>

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 Ron Kreymborg                   Systems Administrator
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