In the vast majority of cases, bass rolloff should be turned OFF, period. If you have a really boomy room it might help, but otherwise, you're doing exactly what the name says: cutting out bass.
I strongly disagree with the sentiment that there's rarely a need for bass roll-off as you can just EQ in post. Bass roll-off is a tool that, if used properly, should be a part of any recordists arsenal.
Bass roll-off is useful in the microphone > recorder signal path because it will increase the dynamic range available to all frequencies present. Rather than try to explain this myself, here is a perfect quote that expresses why roll-off is beneficial:
Removing some of the low frequency energy leaves the system more robust wrt to taking good care of the higher frequencies. The upshot is less strain on power supplies, reduced loss in signal caps, less intermodulation distortion, less harmonics added etc .. "
You can't argue that roll-off, if done properly, isn't beneficial.
However, most bass-roll (especially with the microphones, preamps and battery boxes, and recorders used by the people on this forum) is not done properly hence the fear to use it outside of post-processing. I feel this is primarily a result of the companies marketing products to tapers and their mis-information (or lack of instruction) on how the science of roll-off works.
Bass roll-off values are not static and dependent on the downstream input impedance! For example, many battery boxes commonly marketing with selectable values of bass roll-off are assuming a common input impedance value... typically 10k ohms. If you use a recorder with an input impedance of 10k ohms, great, but many do not. Input impedances of the various recorders can differ as much as 10 fold!!! Some are as low as 4.7k (many Sony mic inputs) and some are as high as 47k (Sony line inputs). 20k is an extremely common value, which effectively halves the roll-off provided. If you've set your bbox to start roll-off at 120 Hz roll-off, the reality is you're starting it at 60 hZ which is hardly the same.
If you don't know the input impedance of your recording device, you won't know the amount of bass roll-off you are actually providing! If you know your recorder's input impedance, but not the assumed value in the product's User manual, you're really just hoping it's a close match to your recorder. I have a big pet peeve with the fact that this isn't clearly documented with every battery box or preamp sold by most/all microphone manufacturers. To do it right, you need to provide a chart of the various recorders' input impedances and keep it updated as new recorders hit the market.
All that aside, I want to reiterate that roll-off is not something to fear, so long as you do it right! Doing it in post is acceptable and much easier, but there are very real benefits to doing it upstream of the recording device which, I feel, are generally misunderstood.
Topic: First recording with PCM-M10 - Very little bass (Read 11283 times)