Re: DWT anti-causality

Jerry Avins wrote:

The filter delay is built into the problem; low frequencies at high
sample rates make for long filters. Downsampling the data is simply an
efficient way to downsize the filter. Using a different filter that
enables you to avoid downsampling won't decrease your delay.

Put differently, you can either downsample the data or increase the
filter length for each pass. That increases memory use but doesn't
change the delay.


Right - I'll end up doubling the filter length for each level and end
up with the same situation. Ok, scratch that idea.

How about my initial one, that didn't work - simply using an expanding
window? For each sample you transform it and the previous samples. You
then only keep the last sample from each transform. I know it is
computationally atrocious, but still, it should eliminate the delay, at
least explicitly. It didn't work for me (i suspect) because of the
boundary problems due to padding, but I'm thinking it's possible to
work around the problem by using such window lengths that no padding is
necessary. In that situation, there will be a delay, but it will be
constant for all decomposition levels.

.

Relevant Pages

  • Re: DWT anti-causality
    ... delay increases exponentially with the decomposition level. ... I'm thinking something along the lines of rather than downsampling the ... Downsampling the data is simply an efficient way to downsize the filter. ...
    (comp.dsp)
  • Re: Downsample and then reconstruct an image.
    ... pixels together (box filter) is somewhat better. ... There is no "best" downsampling filter - it depends on the tradeoffs ... you cannot reconstruct the original image ... frequencies to the larger image size. ...
    (sci.image.processing)
  • Re: Interpolation
    ... lowpass responses narrower than the Nyquist band. ... Downsampling with anti-alias filtering is the only case I've ... for any lowpass anti-aliasing filter designed for sample rate ...
    (comp.dsp)
  • Re: Interchanging of filtering and decimation operations
    ... It is known that downsampling introduces aliasing if the signal to be ... pass filter before it is downsampled. ... or is it always necessary to filter the signal first and then ... When cleverly done filtering and decimation can be combined into one operation. ...
    (comp.dsp)
  • Re: DWT anti-causality
    ... efficient way to downsize the filter. ... enables you to avoid downsampling won't decrease your delay. ... For each sample you transform it and the previous samples. ...
    (comp.dsp)
Loading