Need to remove siren signal
I am working on a project that requires us to filter out siren noise.
The frequencies of the sirens are 375 and 500 with the harmonic, 750, 1000, 1125, 1500 and so on. I was quite successful in filtering it out, but now I hear an annoying click when changing the tone frequency. What are the options to remove the click?
I built up the filtering by applying 2 peak filters per frequency, one of which is placed in anti-phase. The original signal is then added to the filtered signal.
Audio Signal Processors
Audio Products
software
SigmaDSP Audio Processors
adau1701
Hello,
Cancelling the siren frequency via subtracting peak filters is a novel method! I assume it works better than directly using notch filters. By "changing the tone frequency," do you mean that you're adjusting the input siren tones? Or adjusting the DSP filters to better cancel the tones? Let's consider the latter case first.
-------------------------------
The undesired clicks may have several causes. For example, if you're changing frequency via microcontroller, writing the parameters directly invites clicks and pops. In that case, safeloading the parameters instead will prevent this. Safeloading is described in the ADAU1701 data sheet. You need to pay attention to the exact procedure, since any mistake results in a frustrating "it doesn't work" situation.
If you're not changing frequency via micro, then it would help to describe specifically how you're presently changing the filter frequency. Some of the lookup filters available in SigmaStudio include a slew setting, which should smooth over the filter transitions and thus minimize any clicks.
--------------------------------
If your issue is instead clicks when changing the input tones, it could be that the equipment you're using to generate the tones produces some discontinuity in its output upon the frequency change. Such could be drowned out by the tones themselves, yet audible once they're filtered out by your project. You could confirm this by oscilloscope. Or if your hardware is connected to SigmaStudio via USBi, you can try a simple test: Simulate the external siren tones by adding VCOs fed by DC sources to your project. Set the DC sources for your initial siren tones via the formula, DC = 2 f / Fs. Then, with the project running, change one of the DC sources to a new value. The VCO(s) assume the new frequency without any transients. If you still hear clicks, the issue may be the transient response of the filters. You'll need a different filter configuration.
Best regards,
Bob
Please log in to reply.