Question to anyone with a BFD,

Discussion in 'Home Theater Projects' started by Jones_Rush, Jul 27, 2003.

  1. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    198
    Likes Received:
    0
    In the manual of the Behringer Feedback Destoyer, it says that it can attenuate each frequency up to -48db. Now, is there a practical limitation to how much I can attenuate ?, or can I just safely attenuate with full -48db if needed ?. I can't remember where, but I think that I've read somewhere that attenuating with the BFD with more than -12-15db might produce some artifacts. Can anyone confirm ?.
     
  2. Wayne A. Pflughaupt

    Joined:
    Aug 5, 1999
    Messages:
    6,098
    Likes Received:
    33
    Location:
    Katy, TX
    Real Name:
    Wayne
    Jones,

    The question is moot because you won’t need to attenuate anything even close to 48dB. The second question, I’ve seen people use cuts of more than 15dB with no problem.

    Regards,
    Wayne A. Pflughaupt
     
  3. Stephen Dodds

    Stephen Dodds Second Unit

    Joined:
    Aug 29, 1998
    Messages:
    354
    Likes Received:
    0
    But yes, the more you attenuate the more information you lose. The BFD uses digital gain to drop the levels, which means the more you cut the more bits you lose.


    Steve
     
  4. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    198
    Likes Received:
    0
     
  5. Brian Fellmeth

    Brian Fellmeth Supporting Actor

    Joined:
    Jul 30, 2000
    Messages:
    789
    Likes Received:
    0
    Both Wayne and Stephen assumed that you are using the filters to equalize, which is not what you are doing. You are trying to use the filters to create a shelf. I highly recommend you work with the simulator and find the combination of filters that best acomplishes your goal of a low pass shelf at about 40 Hz. By all means dial them all the way to -48 dB, and use a narrow bandwidth.
     
  6. Brian Fellmeth

    Brian Fellmeth Supporting Actor

    Joined:
    Jul 30, 2000
    Messages:
    789
    Likes Received:
    0
    I fired up the simulater, and here is what works. Set 8 filters at 50,55,60,68,75,82,90 and 100 Hz. All minimal width (1/60 Octave), all maximum cut -48dB. The result is down 3 dB at 40, down 8dB at 45 and down at least 30dB from 50 to over 100.

    Your original question about artifacts- not a concern, since your large cuts are to snuff a signal out entirely. The artifact would apply with a large cut in a portion of the signal that is still audible since the engine would not have enough bit depth left to supply a smooth signal to the D to A converter.
     
  7. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    198
    Likes Received:
    0
    Thanks guys.
     
  8. Brian-K-Owens

    Brian-K-Owens Stunt Coordinator

    Joined:
    Feb 6, 2003
    Messages:
    194
    Likes Received:
    0
    I just use 2 bands of mine at 1.6kHz and 2.0kHz @ the widest bandwidth possible with -48dB gain setting (my preamp only has a 100 Hz lowpass filter). Not sure where the net cutoff frequency ends up, but you cannot hear ANYTHING but bass from the sub.

    Brian
     
  9. Wayne A. Pflughaupt

    Joined:
    Aug 5, 1999
    Messages:
    6,098
    Likes Received:
    33
    Location:
    Katy, TX
    Real Name:
    Wayne
    I’ve seen people who applied too many negative filters (when equalizing subs) to the point that the BFD would no longer pass a signal, so this is something you will have to look out for. Perhaps there is a compensation that can be applied (I don’t have a BFD myself)?

    Regards,
    Wayne A. Pflughaupt
     

Share This Page