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High Pass/Low Pass Filters
And should this help get rid of some of the muddiness in my mix?
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It is certainly worthwhile removing unwanted low frequency rubbish which most mic and DI inputs pickup, but which doesn't contribute musically (in most cases) and just robs the playback system of power and headroom. So high-pass filtering is pretty much routine and very worthwhile.
As to the actual turn-over frequency, that depends both on the source and how that source sits in the mix. The fundamental of a four-string bass is theoretically 40Hz or so, as you say, but most of the bass sound in the mix is actually conveyed by the higher harmonics -- some of which may well be stronger in level than the fuindamental, actually.
So it could be, perhaps, that filtering at 80Hz, say -- and even though it will reduce the fundamental -- will help to let the kick drum come through more powerfully without being masked by a flabby bass. And the overall mix could well sound tighter and better as a result. Auditioned in isolation, the bass might sound less powerful than with the HPF set at 40Hz (or lower), but it's the sound of the full mix that counts!
Similarly, it is very common to roll off a lot of the bottom end from acoustic rhythm guitars,m making them sound decidely anaemic in isolation, but they sit much better in the mix without making things sound muddy and congested in the lower mid.
Low pass filtering is less important and less commonly done. You might do it if a source is noisy, and removing some of the high end hiss cleans things up usefully. You might also do it to reduce the harshness of a distortion effect. But as a general rule of thumb, it isn't usually necessary.
So, the answer is yes, high-pass filtering will help to reduce the muddiness in your mix -- but be prepared to set the filter surprisingly high and remember that it's the sound of the full mix that matters, not the individual filtered source!
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Technical Editor, Sound On Sound
The answer, as always, is to use your ears, but a spectrum analyser can be helpful if you're struggling to hear what's going on in the subs. It's all about maximizing the frequencies that are useful to your mix (and so worth using up headroom to reproduce) and removing the frequencies that aren't.
My advice is to not get bogged down by those numbers and think about what you're trying to achieve with what you've been given.
- Jedi Poster
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An Eagle for an Emperor, A Kestrel for a Knave.
If I'm recording through my mixing desk I will often use the 80Hz filter built in to the desk on anything that isn't intended to have any low end.
- James Perrett
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