Jesus man. Think it through.

1) A low pass filter attenuates high frequency sound gradually above the cutoff point.

2) If you listen to a bassdrum and it has lots of high frequency signal energy that you don't want - use a low pass filter to get rid of it.

Filters and orders:

A single pole low pass filter attenuates signal with a frequency above cutoff at a rate of 6dB per octave.

An octave is measured in multiples of a fundamental frequency so if you have a 60hz sine wave, then a sine wave an octave higher will be 120hz. The next octave up is at 240hz.

So if you use a low pass filter on a 60hz saw wave and the filter cutoff is at 60hz then the output level will be -6dB at 120hz, -12dB at 240hz and -18dB 480hz.

A two pole low pass filter attenuates signal with a frequency above cutoff at a rate of 12dB per octave.

A three pole low pass filter = 18dB/octave.

A four pole low pass filter = 24dB/octave.

A six pole low pass filter = 36dB/octave.

Filters with more poles are referred to as higher order filters. You can graph these results and they should be fairly self explanatory.

Use whichever is appropriate to your situation or don't use them at all if you don't need to.

quote:

Originally posted by Derivative Jesus man. Think it through. 1) A low pass filter attenuates high frequency sound gradually above the cutoff point. 2) If you listen to a bassdrum and it has lots of high frequency signal energy that you don't want - use a low pass filter to get rid of it. Filters and orders: A single pole low pass filter attenuates signal with a frequency above cutoff at a rate of 6dB per octave. An octave is measured in multiples of a fundamental frequency so if you have a 60hz sine wave, then a sine wave an octave higher will be 120hz. The next octave up is at 240hz. So if you use a low pass filter on a 60hz saw wave and the filter cutoff is at 60hz then the output level will be -6dB at 120hz, -12dB at 240hz and -18dB 480hz. A two pole low pass filter attenuates signal with a frequency above cutoff at a rate of 12dB per octave. A three pole low pass filter = 18dB/octave. A four pole low pass filter = 24dB/octave. A six pole low pass filter = 36dB/octave. Filters with more poles are referred to as higher order filters. You can graph these results and they should be fairly self explanatory. Use whichever is appropriate to your situation or don't use them at all if you don't need to.

Usefull Info, maybe you can help me figure something out.
Saturday I was generating a pure sine wav at C3 on my piano which is I forget how many hertz. Anyways I put a high pas filter and put the cut off frequency to exactly the hertz at C3. The tone was almost gone but I could still hear sound. I didnt understand why I could still hear sound since a pure wine wave only contains the fundamental frequency. Technically if I cut the fundamental I shouldnt be hearing any other sound since there are no harmonics?

quote:

Originally posted by Dj Nacht Usefull Info, maybe you can help me figure something out. Saturday I was generating a pure sine wav at C3 on my piano which is I forget how many hertz. Anyways I put a high pas filter and put the cut off frequency to exactly the hertz at C3. The tone was almost gone but I could still hear sound. I didnt understand why I could still hear sound since a pure wine wave only contains the fundamental frequency. Technically if I cut the fundamental I shouldnt be hearing any other sound since there are no harmonics?

true, but you have to take the roll off of the filter as said before. In essential a filter on a sine should more or less act like a volume slider when filtering a sine. the lower you put the low pass the lower the volume of the sine would be. It's possible you still hear something. But the character of the sound should change. (allthough some filters colour the sound which could cause the change)

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quote:

If less is more think about how much more more would be. -Frasier

quote:

Originally posted by Dj Nacht Usefull Info, maybe you can help me figure something out. Saturday I was generating a pure sine wav at C3 on my piano which is I forget how many hertz. Anyways I put a high pas filter and put the cut off frequency to exactly the hertz at C3. The tone was almost gone but I could still hear sound. I didnt understand why I could still hear sound since a pure wine wave only contains the fundamental frequency. Technically if I cut the fundamental I shouldnt be hearing any other sound since there are no harmonics?

You need to adjust the filter to a lower (or higher, if you're using a HP filter) frequency and use a filter with a steeper slope, like a 36dB/octave.

I just remembered that I wasnt even using a filter! I was using an EQ with the narrowest Q Value and made a notch cut at C3 Hertz. Im pretty sure if I would have done it with a high pass filter it would have removed all the sound.