ReaFIR

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Revision as of 22:27, 19 February 2007

Main Page > REAPER Documentation > REAPER Effects

ReaFIR is an expansive plug-in that includes an FFT spectrum analysis window! ReaFIR can be used as a precision EQ, a Gate, a fast attack/release precision compressor, a noise reduction tool, and more!

General Controls

ReaFIR has 5 main modes, but before discussing these modes in depth, we'll look at the common controls that affect use.

• The main display: this window shows analysis of the audio being processed, as well as the user-defined parameter curve. This window shows frequencies from left to right (representing 0 Hz to 24kHz), and volumes from top to bottom (representing by default +24dB to -90dB, but you can change this). The red line represents the user defined parameter curve, the dark yellow represents the input signal, and the bright yellow represents the output signal.

• The reset button: this resets the user-define parameter curve to a flat line at +0dB.

• Edit mode: this lets you switch between point-based editing and precise mode (which lets you draw very complex curves). The default is point-based. In point based mode you can create any number of points that define the curve.

• FFT size: This controls what sized blocks are used for processing. In general larger FFT sizes allow more precise effects, and use more CPU. Some modes, however, may be affected in other ways by the FFT size. For example, in the Compressor and Gate modes, larger FFT sizes result in a larger effective attack/release time.

• Curve range adjustment (on the right side of the main display): this allows you to set the range of adjustment allowed.

• Show analysis: disable this if you do not care to see the approximate spectrum of the signal.

• Analysis floor: this lets you choose the lowest value of analysis shown. In general you should keep this set to the same as the low range of the curve range adjustment (above), but sometimes you may want it to be different (i.e. you may want the adjustment range to be +12..-12, but still show the analysis down to -90dB).

• Output gain: lets you adjust the volume of the output, after all processing has occurred.

• Reduce artifacts (less effective): by default ReaFIR operates in a non-linear FFT-based filtering fashion. The downside is that in certain instances the filter can introduce aliasing artifacts, in exchange for extremely high filtering effectiveness. If you check this box, ReaFIR will operate as a FIR filter, meaning it will be limited in its effectiveness by the length of the filter, but will respond linearly and without artifacts.

Some Considerations

• In general you will want to keep the analysis floor at -90dB or more. The floor represents the lowest value it can display and should thus be set to around the noise floor of your set up (-96dB for 16-bit and -144dB for 24-bit). Keeping the adjustment range's floor the same as the analysis floor is often a good idea, especially when you are using the gate/compressor/noise reduction modes.

• Keep in mind that even if the highest point of the analysis is at -20dB, the peak of the signal's volume may be greatly higher, since the audio signal is the sum of all bands.

• ReaFIR's analysis display is an approximation, and has many artifacts of its own (stair-stepping being the most noticeable). This is a result of prioritizing processing efficiency over display quality.

ReaFIR Rundown

There are 5 modes you can use ReaFIR in.

• EQ
• Gate
• Compressor
• Convolve L/R
• Subtract

EQ

In EQ mode, you have the option of using precise lines or points (located in the "edit mode" drop down list). Probably the easiest way to use ReaFIR in EQ mode is to start start with precise mode, draw a rough curve and then switch to points mode. Doing this will keep the general form of the original curve, but it will be 'smartly' converted to points for easy adjustments!

EQ Mode Tips

• Add in as many points as you want simply by clicking on the red line that appears in the analysis window.
• Delete points by holding CTRL and left clicking a point with your mouse.
• Right Click a point and Choose "set" to manually set a point's frequency and gain
• Make a small, narrow cut or boost by setting the analysis floor to -10, then place two points at 0dB along the spectrum that will serve as the maximum and minimum affected area of the cut or boost (this serves the same purpose as adjusting Q in other EQ plugins). Place a third point in between the max/min points and raise or lower that third point to make the cut or boost. For example, to affect a range of 100Hz with a cut in the centre of that range, set 1 point to 300hz at 0dB and another to 400hz at 0dB. Set a third point to 350hz and Lower or raise it's gain to taste.
• hold down shift while changing the gain of a point to make sure you don't accidentally move it across the spectrum.
• Create a ridiculously sharp 80hz High Pass filter by setting one point to 80hz at 0dB, and another point to 79.9hz at -90dB! You can make the filter smoother simply by dragging the point set to 79.9hz across the spectrum (for example, to 40hz).
• You can change the gain of the entire EQ curve (red line) by holding CTRL while dragging any part of the red line up or down with your mouse.
  
  

Gate

In gate mode, the red line acts as a threshold. Think of the threshold in a gate as working opposite to a compressor's threshold. For example, if you set the threshold High in gate mode, less sound will be allowed to pass through the gate, but setting it lower will allow more sound to pass through.

Gate mode can be used for a variety of things, including traditional gating of a track, but also for midi triggering. You can do this by gating out specific bands or frequencies by manipulating the threshold's curve in either precise or point mode!

See the following video for more ReaFIR to the rescue

Compressor

In Compressor mode, ReaFIR acts as a fast attack/release multi band compressor. However, there is a notable difference between a regular multi band compressors and ReaFIR. With ReaFIR, you can choose more specifically which frequencies you want to compress without having to worry about crossover.

You can set the ratio from a very gentle 1.01 to an extremely hard 100:1 using the ratio slider that appears in compressor mode.

ReaFIR's Red line in compressor mode acts as the threshold (in either preside or point mode). Because of the flexibility of this threshold, you are able to choose exactly what gets compression, and can do some very interesting things with it.

• Gradually lower the threshold between 1-2khz so that 1khz gets some compression, but 2khz gets compressed more.
  • Keep in mind that if you lower the threshold too low, you will hear audible distortion from the fast attack/release.
• Define a threshold only below 100hz to compress bass frequencies.
• Define a bell shaped threshold with any Q you want (WOW!- see EQ tips for how-to)
• The FFT window will show you how much gain reduction is happening in grey - the original signal's frequencies will still show as red.
  
• Use the EQ tips above to see the different ways you can manipulate the threshold in compressor mode.
  

Convolve LR

In Convolve L/R mode, ReaFIR does an operation called inverse FFT (IFFT). Without going into too much detail, the process is that ReaFIR compares the Left and Right channels of a stereo signal and multiplies them together. ReaFIR then further processes this with IFFT. The result is that frequencies that are the same on the Left and Right channels re-enforce each other (so you will hear them), while dissimilar frequencies do not - (so they weaken or vanish completely).

So what you will hear in Convolve LR mode is the "like" frequencies from the Left and right channels together and any dissimilar frequencies will be faint or non-existent. This is useful to check the overall balance of a mix to see what is happening sonically - especially if there is too much of a frequency band (in other words, an extreme build-up of like frequencies).

You can also make EQ adjustments in convolve mode using either precise lines or points - which can help you make decisions about what needs to be done within a mix to balance it out.

Subtract

ReaFIR's subtract mode is excellent for Noise Reduction!
when you switch to subtract mode, you will notice a new button that says "automatically build noise profile". To use this function, enable it during a section of ONLY noise and you will see the profile being built. Once you are happy with the noise profile, un-check "automatically build noise profile" and save the preset.

You can then do a number of interesting things with the noise profile:

• Hold CTRL, click and drag the noise profile to raise or lower the entire profile (the higher you raise it, the more artifacts you will hear)
• Try building the noise profile with a larger FFT size than default, and then change the size back to default after you have built the noise profile.
• You are able to change parts of the noise profile, however you will pretty much loose what has been built as a result as there isn't a way (yet!) to add points to the noise profile (i.e. so that you can pivot sections of the noise profile). If you switch to points, the entire profile will be converted.

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