Videogamer555 wrote:Actually the center frequency should never be the logarithmic center. The center of a filter who's upper bound is 10000Hz, and who's lower bound is 100Hz, should NEVER be 1000Hz. At least not for scientific use. Maybe in the music industry, using a logarithmic center frequency is useful. However in SCIENTIFIC use, the LINEAR center is most useful. The linear center between 100 Hz and 10000Hz is 5050Hz. For example if I want to filter frequencies of an electromagnetic signal, blocking everything below 100Hz and above 10000Hz, and having the filter most strongly pass its center frequency, that means I want the signal most strongly passed to be 5050Hz. And before you say that a computer can't receive radio waves, the fact is IT CAN, without any additional hardware than a sound card. The highest frequency that can be received for a 192kHz sampling soundcard is 96kHz. This is near the low end of the LF (low frequency) band of the RF spectrum. To do this, simply plug in an antenna into the microphone or line in port on your soundcard. Then turn up the gain in your Windows mixer control. After recording a segment, you can use software to further boost the signal strength. For processing such a recorded signal I need some decent software. Goldwave is GREAT for this, but it costs money, so I'm just using the demo version and plan to stop using it when the demo version runs out. Meanwhile, I need Audacity (a free program) to have features added to it to make it as usable to me as Goldwave has been. So that's why I'm asking for these features. When the demo version of Goldwave runs out. I'll be fully switching to Audacity for my signal processing needs for my hobby LF, VLF, and ELF radio listening hobby. So that's why I'm trying to get the developers to add in features that I will be depending on for my signal processing needs.
Sounds interesting.
Do you need then a steep bandpass to isolate and demodulate the signal?
You could write down your procedure under a different topic (e.g. as tutorial under the forum Education).
Do you have a sample file that I could experiment with?
The spectral selection has a nice feature:
It can jump from spectral peak to spectral peak.
I've assigned alt + page up/page down for this.
This should make it fairly easy to find a strong modulated signal for example.
We can then write a plug-in that does only use the center information and you can specify the bandwidth on both sides of it for the bandpass filter.
This works of course also with manual selection. You have to draw a narrow rectangle around the carrier (5050 Hz for example).
Or do you prefer to work with the rectangle itself? The center of my Fir filter lies rather in the exact middle than on the geometric mean. That's because the transition width from stop to pass band is for both frequencies the same (could of course be logarithmic as well).
Just tell me what you need.
Robert