Hey everybody, I'm working on some audio post production work right now, using PreSonus Studio One. I wanted to use a high pass on one channel and a low pass on another in such a way that I could then combine them without emphasizing or de-emphasizing any particular frequencies - it's sort of like a crossover in reverse.
Anyway, the weird thing that came up, is that if you choose different filter slopes in Studio One, the frequency you've chosen ends up being attenuated by different amounts. My experience up until now has been that EQ settings, filter cutoffs, microphone specs, etc. are pretty much all described based on their 3dB down points. So, I would've expected a 150Hz HP filter to be 3dB down at 150Hz, regardless of the chosen slope. As it is, one slope yields the expected -3dB at 150Hz. Two of the slopes yield -6dB at 150Hz, and one yields -9dB at 150Hz.
Am I missing something, or is this really strange? At first I thought maybe these filters were being described in terms of the cutoff frequency of a single pole, and then had different responses because of the additional poles, but that doesn't seem to add up either.
Another interesting thing that I discovered is that the filters which are 6dB down at 150Hz can be used, in conjunction with a 150Hz LP filter, to achieve my "reverse-crossover" system with near-perfect results... but the filter which is 3dB down at 150Hz behaves unexpectedly. I'd expect the combo of two channels that are down 3dB at 150Hz to result in a signal that boosted 3dB at 150Hz. Instead, the result is a perfect null at 150Hz. I'm guessing that this filter has a 90 degree phase shift at the 3dB down point, and that combining two filters with a +90 and -90 phase response results in perfect cancellation.
So, in terms of accomplishing what I need to musically, I can just use the 6 or 24dB/octave filters and get the desired results, but I'm very curious about the naming/labelling of these filters, and the apparent phase response implications, with one filter cancelling completely and two other filters appearing to work perfectly.
Any thoughts? Am I wrong to expect these filters to be described by their 3dB down point?
Anyway, the weird thing that came up, is that if you choose different filter slopes in Studio One, the frequency you've chosen ends up being attenuated by different amounts. My experience up until now has been that EQ settings, filter cutoffs, microphone specs, etc. are pretty much all described based on their 3dB down points. So, I would've expected a 150Hz HP filter to be 3dB down at 150Hz, regardless of the chosen slope. As it is, one slope yields the expected -3dB at 150Hz. Two of the slopes yield -6dB at 150Hz, and one yields -9dB at 150Hz.
Am I missing something, or is this really strange? At first I thought maybe these filters were being described in terms of the cutoff frequency of a single pole, and then had different responses because of the additional poles, but that doesn't seem to add up either.
Another interesting thing that I discovered is that the filters which are 6dB down at 150Hz can be used, in conjunction with a 150Hz LP filter, to achieve my "reverse-crossover" system with near-perfect results... but the filter which is 3dB down at 150Hz behaves unexpectedly. I'd expect the combo of two channels that are down 3dB at 150Hz to result in a signal that boosted 3dB at 150Hz. Instead, the result is a perfect null at 150Hz. I'm guessing that this filter has a 90 degree phase shift at the 3dB down point, and that combining two filters with a +90 and -90 phase response results in perfect cancellation.
So, in terms of accomplishing what I need to musically, I can just use the 6 or 24dB/octave filters and get the desired results, but I'm very curious about the naming/labelling of these filters, and the apparent phase response implications, with one filter cancelling completely and two other filters appearing to work perfectly.
Any thoughts? Am I wrong to expect these filters to be described by their 3dB down point?