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| WaveWarp 2.0 Component
      
Multirate:
Functional Description
Increases the sample rate of the input by a factor of 2, with
a built-in IIR anti-imaging filter.
The output sample rate is twice the
input sample rate. This component is identical in function
to the low-frequency synthesis
branch of a two-channel IIR filter bank (hence the name "Lo").
Algorithm
In the current implementation, the IIR low-pass
anti-imaging filter is
"hard-wired" (i.e. cannot be changed by the user).
It is designed and implemented according to the method
described in
[VaCo].
Concerning the particulars of this method for the present
application, it is found that the use of two cascaded elementary
all-pass sections is sufficient for reasonable performance.
The upsampler implementation
is highly-efficient, since the use of all-pass subfilters allows
the system to be structured in polyphase form (not generally possible
for IIR filters)
such that the filtering is computed at the lower
(i.e. the input) sample rate.
The end result is the same as if the
filtering was performed last (i.e. at the higher sample rate), preceded
by the upsampling (inserting (M-1) zero-valued
samples between successive inputs). The real-time output from
each polyphase IIR filter branch is computed by direct
evaluation of the cascaded all-pass elements.
See
[CrRa]
and
[StNg]
for a detailed treatment
of multirate signal processing.
For a specific discussion
on upsampling by an integer factor, see
section 2.3.2 of
[CrRa]
and chapters 1 & 3 of
[StNg].
For a specific discussion
on two-channel filter banks (FIR only), see
[StNg]
chapter 4.
For design methodologies for
IIR (recursive) filters suitable for sample rate conversion,
see, for example,
[VaCo],
[ReSa1],
and
[ReSa2].
Signal Implementations
| Audio signals | Control signals | Description |
|---|
| Single input mono single output mono | n/a | Converts the sample rate of the mono signal |
| Single input stereo single output stereo | n/a | Converts the sample rate of the stereo signal |
Related components:
Example DrawingBoards illustrating usage:
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