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Low Pass Filter
This filter is called a Low-pass filter because it only passes through signals that are lower than its set corner frequency. It attenuates high frequency signals above the corner frequency.
The effect can be similar to turning down the treble control on a home stereo except that the Low-pass filter is much more flexible. This filter can be somewhat useful for reducing hiss in a recording, but care must be taken not to reduce the "presence" of a recording by eliminating too much of the high end musical content at the same time.
Low Pass Filter with Chebyshev or Butterworth Response with up to a 4th Order Response (Slope)
This type of filter is most useful when a recording does not contain any useful sonic information above a certain frequency, and you wish to attenuate that high frequency noise that would otherwise be present.
This is a digital simulation of a conventional Low-pass filter. It is created using an Infinite Impulse Response (IIR) algorithm having a Butterworth or Chebyshev characteristic (for the higher order slopes). Frequencies below the "corner frequency" are passed through to the output, and frequencies above the corner are attenuated. The degree to which higher frequencies are attenuated is determined by the slope (order) of the filter. Four slopes are provided. They are 6dB / Octave, 12 dB / Octave, 18 dB / Octave and 24 dB / Octave. The higher the slope, the more attenuation will occur to frequencies above the corner frequency. The corner frequency is the frequency that you choose, and it is defined as the frequency at which the signal has been attenuated by 3 dB relative to the pass-band. This filter can be somewhat useful for reducing hiss in a recording, but care must be taken not to reduce the presence of the recording by eliminating too much of the high-end musical content at the same time. When used selectively, this filter can also be used either to "De-Ess" an overly sibilant vocal, or reduce harsh harmonic distortion products that may have resulted from occasional master recording overloading (clipping). For forensic recordings, this filter can be used to remove most noise sounds whose frequencies are above the speech spectrum by setting the corner frequency to somewhere between 3,000 to 4,500 Hz. The use of steep slopes (& Chebyshev) are often very useful in these forensics audio situations.
The Low Pass Filter
The higher order (12, 18, & 24 dB / Octave) Low-pass filters are of the Butterworth or Chebyshev types, depending on your choice.
The following is a summary of the control parameters and range of adjustment provided for the Lowpass Filter:
Important 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 an 11.025 kHz sampling rate, this value will drop to 5 kHz.
Lowpass Filter Operating Procedure (Tutorial)
This filter is called a Low-pass filter because it only passes through signals that are lower than its set corner frequency. It attenuates high frequency signals above the corner frequency.
The effect can be similar to turning down the treble control on a home stereo except that the Low-pass filter is much more flexible. This filter can be somewhat useful for reducing hiss in a recording, but care must be taken not to reduce the "presence" of a recording by eliminating too much of the high end musical content at the same time.
Low Pass Filter with Chebyshev or Butterworth Response with up to a 4th Order Response (Slope)
This type of filter is most useful when a recording does not contain any useful sonic information above a certain frequency, and you wish to attenuate that high frequency noise that would otherwise be present.
This is a digital simulation of a conventional Low-pass filter. It is created using an Infinite Impulse Response (IIR) algorithm having a Butterworth or Chebyshev characteristic (for the higher order slopes). Frequencies below the "corner frequency" are passed through to the output, and frequencies above the corner are attenuated. The degree to which higher frequencies are attenuated is determined by the slope (order) of the filter. Four slopes are provided. They are 6dB / Octave, 12 dB / Octave, 18 dB / Octave and 24 dB / Octave. The higher the slope, the more attenuation will occur to frequencies above the corner frequency. The corner frequency is the frequency that you choose, and it is defined as the frequency at which the signal has been attenuated by 3 dB relative to the pass-band. This filter can be somewhat useful for reducing hiss in a recording, but care must be taken not to reduce the presence of the recording by eliminating too much of the high-end musical content at the same time. When used selectively, this filter can also be used either to "De-Ess" an overly sibilant vocal, or reduce harsh harmonic distortion products that may have resulted from occasional master recording overloading (clipping). For forensic recordings, this filter can be used to remove most noise sounds whose frequencies are above the speech spectrum by setting the corner frequency to somewhere between 3,000 to 4,500 Hz. The use of steep slopes (& Chebyshev) are often very useful in these forensics audio situations.
The Low Pass Filter
The higher order (12, 18, & 24 dB / Octave) Low-pass filters are of the Butterworth or Chebyshev types, depending on your choice.
The following is a summary of the control parameters and range of adjustment provided for the Lowpass Filter:
- [*=1]Frequency: 5 - 19,999 Hz [*=1]Filter Slope: 6, 12, 18 & 24dB / Octave [*=1]Preview Mode Button: On / Off (The slider control can be adjusted "live" when preview mode is on.) [*=1]Filter Type: Choice of Butterworth or Chebyshev
Important 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 an 11.025 kHz sampling rate, this value will drop to 5 kHz.
Lowpass Filter Operating Procedure (Tutorial)
- Highlight the portion of your .wav file on which you desire to apply the Low-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 "Low-pass."
- Choose the "Frequency" above which you desire to attenuate all signals, utilizing the left mouse button in conjunction with the "Frequency" slider control. When the control is all the way down, the setting will be 5 Hz, and when it is all the way up, the setting will be 19.999 kHz. (Useful settings will usually fall somewhere within the 3 kHz to 15 kHz range, depending on the source material and the goals of the audio restoration.) If you desire finer frequency resolution, you may also use direct numeric entry of the value.
- Choose the Filter "Slope" which you desire. Click on 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 above the "Frequency" setting.
- 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.)
- As the filter is running in either Preview mode or Run mode (Destination File Mode), you will see a dialog box which indicates the "% Done" of the filter algorithm on the selected portion of the Source .wav file. Also, at the top of the Dialog box you will see indicated the "Total Samples to Process:"
- Keep adjusting the Frequency and Slope parameters and testing the various settings using the "Preview" mode until you are satisfied with your results.
- When you are satisfied with a group of settings, you will be done with Preview mode.
- Click on “Run”, and the filter will process your Source .wav file through the 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.