On 11/2/13 6:58 PM, Wen Xue wrote:
But, soft-clipping is not going to change periodicity, is it?
it should not. that's why we don't want non-harmonic components
(aliases) to survive the soft-clipping process.
the point is that if you upsample, then soft-clip, then LPF, and finally
downsample back to the original sample rate, you need only prevent the
aliases from getting back into your *original* baseband. it doesn't
matter that *some* of the images have folded over and become
non-harmonic aliases, just as long as they do not survive into the final
output.
i don't know how better to explain it, without a drawing.
bestest,
r b-j
So if you soft-clip a sine wave, be it polynomial or not, the outcome
is periodical at the same period, so contains only perfect harmonics.
It cannot behave in the "folded alias" way one usually suspect.
On 02/11/2013 06:36, robert bristow-johnson wrote:
just to be clear. the general rule is that an Nth-order polynomial
can generate images at frequencies up to the Nth multiple of the
frequency of the original baseband image. it is sufficient to
oversample by a factor of (N+1)/2 to prevent any of these generated
images from potentially folding back into the baseband. e.g.
3rd-order softclipping requires upsampling by a factor of 2. another
e.g. 7th-order softclipping requires upsampling by a factor of 4 to
avoid any folded aliases from contaminating the original baseband.
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