Topic: Quick Question about Bass Roll Off Feature

[VH Drummer]

I have a quick question before I get my stuff ready for tonight for Velvet Revolver. I was able to borrow a battery box w/ bass roll off from someone here. Today I was recording my band practice with the roll off set at 195Hz but I didn't notice any difference in the recording with or without the rolloff. How does it actually work? Does the rolloff begin when the sound reaches 195Hz or is that the limit? I just don't want this recording to sound like my Supernova one.

Thanks.

[guysonic]

I have a quick question before I get my stuff ready for tonight for Velvet Revolver. I was able to borrow a battery box w/ bass roll off from someone here. Today I was recording my band practice with the roll off set at 195Hz but I didn't notice any difference in the recording with or without the rolloff. How does it actually work? Does the rolloff begin when the sound reaches 195Hz or is that the limit? I just don't want this recording to sound like my Supernova one.

Thanks.

MOST bass rolloff filter boxes require a particular low impedance input typical of MIC input on most decks. 

If you use the LINE input with 10 times less input loading, the filter has up to 10 times LOWER operating filter frequency. 

This may be the reason you cannot hear any difference with filter being in/out because it may be now operating at 19.5Hz where it will make NO audible difference.

[DSatz]

VH Drummer, the frequency given for a filter is almost always the filter's "-3 dB point." That's the frequency at which the filter would reduce the output power by half, if you were to drive something such as a loudspeaker with the signals from your preamp.

Cutting audio power in half, however, doesn't give a big reduction in perceived volume. The main effect of the filter will be at frequencies well below its -3 dB point. For example, an octave below 195 Hz is 97.5 Hz. If your filter is a simple "single-pole" filter, its response should be about 9 dB down at that frequency (-3 dB, plus a further -6 dB for the octave). 9 dB is a considerable reduction--anyone with ears could hear it.

But the perceived result still depends on what you're picking up and how it's being listened to. If the sound that you're picking up has 20 dB more energy at 97.5 Hz than anyone would ever want, the result will still have 11 dB too much there. People would mostly still react to how "too much" that is. Still, in most normal situations you would certainly hear the effect of a 195 Hz filter even if it is just single-pole. And many filters are "steeper"--they cut the low frequencies more severely below their -3 dB point, e.g. 12 dB per octave. Do you know which kind yours is?

Guysonic could well be right if the circumstances he describes are true in your case--if the filter is of a simple, passive design, and you're feeding in signals with very different impedance from what that filter was designed for. That would definitely shift the "corner frequency" (the -3 dB point) of the filter.

--best regards