Signal Processing

Modems

I’m working on a series of articles on modems. It’ll be a loose collection of posts, and not a true multi-part article such as the one on tomography. Modem technology is not widely known and/or understood, even by a technical audience. However…

Submitted on 13 February 2019
Applying a Filter in Both Directions Makes it Zero Phase

Figure 2. Block pulse filtered in both directions.

I’d like to add another trick to your digital filter toolbox: when you apply any filter in both directions on your input signal, the combined filtering operation is zero phase. As you know from…

Tom Mon, 04/23/2018 - 10:23
Apply a Filter Twice for Greatly Improved Performance

Figure 3. Impulse response of the filter of Figure 1 convolved with itself.

Say that you have implemented a low-pass FIR filter with the correct cut-off frequency and transition band, but that you are not quite happy with the suppression of frequencies in the stop band. A straightforward trick to put in your toolbox is that you can double the suppression by…

Tom Mon, 02/26/2018 - 13:01
The Phase Response of a Filter

Figure 2. Frequency (left) and phase (right) response of a moving-average filter.

The article Why use Symmetrical FIR Filters with an Odd Length? mentiones that symmetrical FIR filters are linear phase. In this follow-up article, I simply want to show you what the phase response of these filters actually looks like…

Tom Thu, 02/08/2018 - 17:39