Hi-pass filters on the master fader?

Posted: Wed Apr 30, 2008 1:09 pm

High Pass Filters?

I was looking at a frequency analyzer while playing a few commercially released tunes. I noticed a stark drop-off around 20 kHz.

Is anyone out there using a high pass filter at 20 k? If so, why?

Thanks,

ENW

Posted: Wed Apr 30, 2008 1:19 pm

I'm listening to a record with a high pass filter on 20 kHz right now. It's called silence.

I'm assuming you mean 20 Hz?

Posted: Wed Apr 30, 2008 1:32 pm

Or Low Pass filter...dessimation filter...brick wall filter for DAC??

Posted: Wed Apr 30, 2008 1:41 pm

ENW wrote:

I noticed a stark drop-off around 20 kHz.

Dogs don't buy cd's. Can you hear beyond 20kHz? I know I can't. With my hearing degradation. I have trouble hearing beyond 15k.

Posted: Wed Apr 30, 2008 6:20 pm

Commercial tunes off a standard CD - there's an LPF in place prior to the Nyquist freq. (Nyquist = 22.05K (half the sampling rate @ 44.1k)).

In short, yes - we are using an LPF around 20k.

For future reference -
An LPF (Low Pass Filter) cuts out high frequencies.
An HPF (High Pass Filter) does the opposite.

Posted: Wed Apr 30, 2008 8:06 pm

Hello Bent,

Sorry, I meant low-pass filter.

You da man. Thanks for your expert advice. That's what I suspected from what I was seeing on the analyzer. My degree is in music. I did not know this about Nyquist...

"In order to recover all Fourier components of a periodic waveform, it is necessary to use a sampling rate at least twice the highest waveform frequency. The Nyquist frequency, also called the Nyquist limit, is the highest frequency that can be coded at a given sampling rate in order to be able to fully reconstruct the signal (Wolfram Math World)."

LPF at half the sampling rate. Got it.

Thanks again,

ENW

Posted: Wed Apr 30, 2008 8:39 pm

Posted: Wed Apr 30, 2008 9:55 pm

And a HPF at 10. Just to keep the audiophiles happy and the subsonic-DC-offset-esque crap away.

No?

Posted: Thu May 01, 2008 12:09 am

codemonkey; the ear cannot process pitch information below 20hz.
in musical terms, there are no notes down there, so we
may call the subsonic component "noise".

subsonic signals also stress out the playback amp much more
than audible freqs. so "unheard" (but perhaps felt) subsonics
may cause a playback amp to distort at lower overall
levels.

for these reasons, we may wish to apply hp filters in mastering but
probably not eliminate subsonics entirely, as many instruments
do produce subsonics; and taking into account that timbre
can be affected by removing or adding noise.

my advice here: use your ears, not your eyes to
make this judgement call.

jeff dinces

Posted: Thu May 01, 2008 10:37 am

Back in the 70's I had a friend who had built a big sub for his stereo system and had some way of sending a 5 Hz to it. If you didn't know he was doing it you couldn't really "hear" it, but you could sense something was wrong. He used to joke that he played it when his mother in law came over.

Posted: Thu May 01, 2008 10:43 am

Oh man. 5Hz sine waves rattling your windows and walls.

Can dogs hear that low or is it only 20kHz+?

Posted: Thu May 01, 2008 10:44 am

I have a friend who is a church organist. He says you can't hear the really low pipes but you can feel them hit you in the chest.

That's a hoot about the mother in law.

Posted: Thu May 01, 2008 10:50 am

Times like this I wish we had a real organ. It's a keyboard/electric organ thing which has a nice sound via the Line Out but lacks in physical presence. It's tucked into a corner which sucks, and until I got hold of it, it sounded lousy.
The PA can't help with the LF stuff (it fills the church well enough) but I roll off the lows and add some mid/highs using the better placed speakers.
Sounds crap in recordings but good enough on Sunday mornings.
(If I want a non-rolled off version I need to hijack the Insert)

Shows you the difference 5Hz makes though.

Posted: Thu May 01, 2008 10:59 am

ENW wrote:

I have a friend who is a church organist. He says you can't hear the really low pipes but you can feel them hit you in the chest.

That's a hoot about the mother in law.

One of the organs I record regularly has a few real 32' pipes and a couple digital 32s and digital 64s (yup...64s). The nice thing is, the space is big enough to really get those 64s working with the room. When they kick in, you can feel the marble vibrate. Of course, the other 9500+ *real* pipes don't hurt with that either...

Yeah, you'll definitely feel the vibes from the biggest pipes...
Smile

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