Audacity Forum

cyrano wrote:

HarryHogge wrote:Audicity recommends 24dB rolloff and 20-30hz cutoff.

Can someone explain to me what this means? What happens when the rolloff is higher? Or the cutoff?

The filter will act from 30 Hz down.

Well no, actually. Perhaps counterintuitively, with pass filters the cut-off is the frequency where 3dB of attenuation has already occurred.

A 24 dB rolloff is the steepness of the filter. Back in analog days, 6 or 12 was usually the choice. 18 or 24 was much harder. In the digital world, it doesn't matter.

Hmmm. Not even digital filters are perfect, and as a general rule the steeper the roll off the more unwanted artifacts are produced. There is also a negative psychoacoustic effect of steep filters, although I will grant you that could well not be an issue with subsonic frequencies, hard to test experimentally, however, given you would need en enormous PA sound system!

A mic or RIAA preamp has to be able to take a 1 millivolt signal to 1,000 millivolt, ideally. That's a lot of gain. And doing that without hissing and puffing, can't be done by a lot of the lesser preamps. If you feed those a good signal, it'll work. But if you feed those a weak signal, polluted with rumble and noise, they will add noise and distortion and what comes out isn't usable anymore.

Are you sure about that or do you have any kind of supporting link? I have to tell you, when I read that passage the flashing sirens and alarm bells were going into overdrive on my bullshit detector!

I'm going to use the low cut filter on my ART interface instead of any audacity filters.
In case anyone wanted to know.

HarryHogge wrote:I'm going to use the low cut filter on my ART interface instead of any audacity filters.
In case anyone wanted to know.

The Low Cut on the Art interface does the same job, and will save you time and effort. Unfortunately the Art manual does not say what the cut-off frequency is, or how fast it rolls off low frequencies, but as this interface is designed for phono input, it will hopefully be around 20 Hz cut-off and steep enough to be effective. The important thing to check is that it does not reduce bass in the music.

steve wrote:

HarryHogge wrote:I'm going to use the low cut filter on my ART interface instead of any audacity filters.
In case anyone wanted to know.

The Low Cut on the Art interface does the same job, and will save you time and effort. Unfortunately the Art manual does not say what the cut-off frequency is, or how fast it rolls off low frequencies, but as this interface is designed for phono input, it will hopefully be around 20 Hz cut-off and steep enough to be effective. The important thing to check is that it does not reduce bass in the music.

No bass reduction at all. And to be honest, I can't tell anything really (Not that you can tell when subsonics are removed).
All I know is what's left is a nice clean recording with tight bass (depending on the record, of course).

Look at the meters when the needle is in a silent groove...

Alternatively, switch to spectral view and try to grok the picture. Use a not-so-good record, fi one that has a badly centered hole or is a bit warped.

Shaky wrote:

cyrano wrote:

HarryHogge wrote:Audicity recommends 24dB rolloff and 20-30hz cutoff.

Can someone explain to me what this means? What happens when the rolloff is higher? Or the cutoff?

The filter will act from 30 Hz down.

Well no, actually. Perhaps counterintuitively, with pass filters the cut-off is the frequency where 3dB of attenuation has already occurred.

Here is a graph from High Pass Filter - Audacity Manual that might clarify what happens:




Gale