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Band Pass Filter
Band-pass filters are essentially a combination of a Low-pass filter and a High-pass filter operating together. It attenuates both the high frequency and the low frequency portions of the audio spectrum. It is useful where the recording contains extraneous noise in the low frequency region such as rumble or thumps, and high frequency noise such as hiss. This filter can also be very useful for improving the intelligibility of audio recordings, especially speech, by eliminating the unnecessary portion of the audio spectrum that is not used by speech frequencies to carry useful information to the listener.
The Band Pass Filter
Band Pass Filter with Chebyshev or Butterworth Response with up to 4th Order Slope
This is a digital simulation (IIR based) of a conventional analog Band-pass filter having a Butterworth or Chebyshev response when set to the steeper slope values. Band-pass filters are passive to frequencies within the Band-pass region, but they attenuate frequencies above and below the two corner frequencies. Band-pass filters have both an upper and a lower corner frequency, and like the Low-pass and the High-pass filter, the corner frequencies are defined as the frequencies at which the signals either above the upper corner or below the lower corner are attenuated by 3 dB. Four slopes are provided for the Band-pass Filter, just like the Low-pass and the High-pass. They are 6 dB / Octave, 12 dB / Octave, and 18 dB / Octave and 24 dB / Octave. This filter can be very useful for improving the intelligibility of audio recordings, especially speech, by only passing through signals in the portion of the audio spectrum involved in human speech. The Forensics Menu “Brick Wall” filter has a much steeper version of this filter for dealing with extreme cases of out-of-band noise that needs to be eliminated.
Note:
The higher order (12, 18, & 24 dB / Octave) Band-pass filters are of the Butterworth or Chebyshev type depending on your choice.
Special effects can be produced with the Band-pass filter. These special effects can be useful when producing movies or stage plays or shows and a particular sound producing device and its environment needs to be accurately reproduced through the "House" P. A. System. Here are a few examples:
You can create your own simulations of sound devices and acoustic environments through experimentation with the Band-pass filter parameters. Using the above simulations, in conjunction with the DCArt10 / DCForensics10 reverb, you can further enhance various acoustical environments. Once you discover the appropriate values, write them down or store them as presets for future reference.
Cascading this filter (using the Multi-Filter) with others like the Virtual Valve Amplifier to add distortion, and the Reverb to add room acoustical effects can further embellish these sound simulations.
The Band-pass filter can also be used as a tool to determine if any useful audio information exists in a particular portion of the audio spectrum; it becomes sort of an audible wave analyzer when used in this manner. For more information on this mode of operation, refer to the "Using DCArt10/DC Forensics10 as an Audio Waveform Analyzer" portion of the "How Do I" section of this manual or go to the section which explains the operation of the Spectrum Analyzer.
The following is a summary of the control parameters and range of adjustment provided for the Band-pass Filter:
Note: The frequency range of adjustment up to 19,999 Hz is only effective when utilizing a 44.1 kHz sampling rate. At a 22.05 kHz sampling rate, the maximum effective frequency setting will be 10 kHz, and at a 11.025 kHz sampling rate, this value will drop to 5 kHz.
Band-pass Filter Operating Procedure (Tutorial)
Note 1: If the low frequency control is set to a higher frequency than the high frequency control setting, a "no pass" filter will be created. This is of little useful value, but is allowable by DCArt10/DC Forensics10.
Note 2: You can select Chebyshev rather than Butterworth if you want a steeper filter response at the expense of some ripple within the filter pass-band.
Band-pass filters are essentially a combination of a Low-pass filter and a High-pass filter operating together. It attenuates both the high frequency and the low frequency portions of the audio spectrum. It is useful where the recording contains extraneous noise in the low frequency region such as rumble or thumps, and high frequency noise such as hiss. This filter can also be very useful for improving the intelligibility of audio recordings, especially speech, by eliminating the unnecessary portion of the audio spectrum that is not used by speech frequencies to carry useful information to the listener.
The Band Pass Filter
Band Pass Filter with Chebyshev or Butterworth Response with up to 4th Order Slope
This is a digital simulation (IIR based) of a conventional analog Band-pass filter having a Butterworth or Chebyshev response when set to the steeper slope values. Band-pass filters are passive to frequencies within the Band-pass region, but they attenuate frequencies above and below the two corner frequencies. Band-pass filters have both an upper and a lower corner frequency, and like the Low-pass and the High-pass filter, the corner frequencies are defined as the frequencies at which the signals either above the upper corner or below the lower corner are attenuated by 3 dB. Four slopes are provided for the Band-pass Filter, just like the Low-pass and the High-pass. They are 6 dB / Octave, 12 dB / Octave, and 18 dB / Octave and 24 dB / Octave. This filter can be very useful for improving the intelligibility of audio recordings, especially speech, by only passing through signals in the portion of the audio spectrum involved in human speech. The Forensics Menu “Brick Wall” filter has a much steeper version of this filter for dealing with extreme cases of out-of-band noise that needs to be eliminated.
Note:
The higher order (12, 18, & 24 dB / Octave) Band-pass filters are of the Butterworth or Chebyshev type depending on your choice.
Special effects can be produced with the Band-pass filter. These special effects can be useful when producing movies or stage plays or shows and a particular sound producing device and its environment needs to be accurately reproduced through the "House" P. A. System. Here are a few examples:
| Simulation | Low Freq. Control | High Freq. Control | Slope |
| 1930's Vintage Table Top Radio: | 830 Hz | 2000 Hz | 18 dB / Octave |
| Modern cheap Table Top Radio: | 265 Hz | 6100 Hz | 18 dB / Octave |
| Loud "Walkman" personal stereo as heard by person nearby: | 3650 Hz | 9800 Hz | 18 dB / Octave |
| Modern Stereo System as heard from the next room: | 95 Hz | 4100 Hz | 12 dB / Octave |
| 1950's Vintage Juke Box: | 30 Hz | 2700 Hz | 12 dB / Octave |
| AM Transistor Pocket Radio: | 1395 Hz | 2110 Hz | 18 dB / Octave |
| Telephone Receiver sound from "off the hook": | 2700 Hz | 2895 Hz | 18 dB / Octave |
| Night Club Band as heard from Parking Lot: | 85 Hz | 240 Hz | 12 dB / Octave |
| Old Acoustic Phonograph: | 870 Hz | 2390 Hz | 18 dB / Octave |
| Public Address System at Outdoor Event: | 300 Hz | 3000 Hz | 12 dB / Octave |
| Modern High End Audio System: | 15 Hz | 19,999 Hz | 6 dB / Octave |
| Bandpass Filter Response Limits: | 5 Hz | 19,999 Hz | - |
Cascading this filter (using the Multi-Filter) with others like the Virtual Valve Amplifier to add distortion, and the Reverb to add room acoustical effects can further embellish these sound simulations.
The Band-pass filter can also be used as a tool to determine if any useful audio information exists in a particular portion of the audio spectrum; it becomes sort of an audible wave analyzer when used in this manner. For more information on this mode of operation, refer to the "Using DCArt10/DC Forensics10 as an Audio Waveform Analyzer" portion of the "How Do I" section of this manual or go to the section which explains the operation of the Spectrum Analyzer.
The following is a summary of the control parameters and range of adjustment provided for the Band-pass Filter:
- Low Frequency: 5 - 19,999 Hz.
- High Frequency: 5 - 19,999 Hz.
- Filter Slopes: 6, 12, 18, & 24 dB / Octave.
- Preview Mode Button: On/Off (The slider controls can be adjusted "live" when preview mode is on.)
- Filter Type: Choice of Butterworth or Chebyshev
Note: The frequency range of adjustment up to 19,999 Hz is only effective when utilizing a 44.1 kHz sampling rate. At a 22.05 kHz sampling rate, the maximum effective frequency setting will be 10 kHz, and at a 11.025 kHz sampling rate, this value will drop to 5 kHz.
Band-pass Filter Operating Procedure (Tutorial)
- Highlight the portion of your .wav file on which you desire to apply the Band-pass filter. (You may choose to highlight the entire file or any portion thereof.)
- Click on the “Filter Menu” with the left mouse button.
- Click on "Band-pass."
- Make an initial determination of what band of frequencies you desire to pass through the Band-pass filter.
- Utilizing the right mouse button in conjunction with the Low Frequency slider control, select the lower corner frequency of the range that you have chosen. (The range for this control is 5 Hz to 19.999 kHz)
- Utilizing the right mouse button in conjunction with the High Frequency slider control, select the upper corner frequency of the range that you have chosen. (The range for this control is 5 Hz to 19.999 kHz)
- If you desire finer frequency resolution for either the lower or the upper corner frequency, you may use direct numeric entry, instead of the slider controls.
- Choose the “Filter Slope" which you desire. This slope will symmetrically affect both the upper and lower corner roll-off rates. Click on either 6 dB / Octave, 12 dB / Octave, 18 dB / Octave or 24 dB / Octave. The steeper the slope, the higher will be the degree of attenuation of all frequencies outside of the selected pass band range.
- If you desire to hear the results of your filter settings before creating a new "Destination" file, click on "Preview".
- After a short delay, you will hear the effect of the settings that you have chosen. (The system may seem to stutter if your computer is too slow to keep up with the algorithm in real-time. However, this repeating pattern will not be present in the final Destination processing of the filter.)
- Keep adjusting the Low Frequency and High Frequency sliders as well as the Slope parameters until you achieve the effect you desire and are satisfied with the results.
- When you are satisfied with a group of settings, you will no longer need to invoke the Preview function.
- Click on “Run”, and the filter will process your Source Wave file through the Band-pass Filter algorithm, and create a Destination .wav file containing the output of the filter.
- When this process is complete, you will see the Destination File become highlighted in Yellow, at the same time that the Source File becomes unselected.
- Click on "Close"
Note 1: If the low frequency control is set to a higher frequency than the high frequency control setting, a "no pass" filter will be created. This is of little useful value, but is allowable by DCArt10/DC Forensics10.
Note 2: You can select Chebyshev rather than Butterworth if you want a steeper filter response at the expense of some ripple within the filter pass-band.