Are there types of sound filters that could remain unsaturated while leaving the monitored frequency range undisturbed?
It all dipends on the dynamic range of your recording system. If this is large enough, you can easily apply a severe high pass filter, after recording, for removing the unwanted low frequency background noise.
If, for example, your digital recording system has a dynamic range of 70 dB (which is what you get, more or less, purchasing a low-cost digital recorder, such as a Zoom H4n), and you manage to make a recording without any clipping, you will be able to attenuate the background noise as much as you want, but of course, the level of the high.frequency pitch which you are recording must be within the 70 dB dynamic range. If not, you cancel the unwanted noise, but you are not recording the signal which you want t get.
Let's make an example:
- Low frequency noise: 100 dB
- high-frequency tone: 50 dB
- full scale of the recorder (clipping limit): 120 dB
If the crest factor of the background noise does not exceed 20 dB, the recorder will not clip during recording.
Then you apply an high-pass (or a shelf filter) so that the background noise is reduced by 120 dB, and practically disappear.
Such a digital filtering is easily performed inside any decent waveform editor, such as Adobe Audition or Audacity (the latter is free and open source).
But the high frequency tone is still quite weak, resulting in the recording at -70 dB below the clipping limit. Such a weak signal is at the lower usable boundary of your system, perhaps you can still get some useful information from it, but most probably not.
For ameliorating the situation (or managing the case in which the SPL of the low-frequency noise is bigger, and the SPL of the high-frequency tone is smaller), you need a recording system with a better dynamic range, NOT a better high-pass filter...
The problem is the dynamic range of the recording system (mostly the microphone, but also the preamplifier . The A/D converters, nowadays, is usually 24 bits, so this does not limit the dynamic range).
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