EFFECTS

Fruity Convolver (Convolution, Convolution Reverb & Linear Phase EQ)

Fruity Convolver is a real-time Convolution plugin that can be used to add reverberation, create special effects, apply an acoustic impulse (audio signature) captured from audio equipment/plugins or perform as a linear phase equalizer. When convolving, Fruity Convolver applies the sonic character of one sound to another by convolution of the input audio with an impulse response. The impulse response is an audio recording of an impulse sound after it has bounced off something, bounced around a room (reverberation), passed through an electronic circuit (soaking up the magic within), passed through a plugin (sampling the effect) or any combination of the preceding events. Alternatively, impulse responses can be synthesized or simply another audio file (experiment!).

The convolution process is little more complex than multiplying every sample at the plugin input by the samples in the impulse response. This means that each sample of the input audio triggers the playback of a copy of the impulse response, where all the samples in the impulse response are multiplied by the value of the input sample (-1 to +1). In other words, if the input audio is a single click, 1 sample at 100%, then you will hear the original impulse response. If the impulse response is a single 100% click 5 seconds after the start of the file, you will hear an echo of the input audio delayed by 5 seconds.

Most commonly convolution is used to reproduce the reverberation captured from real acoustic spaces you wouldn't normally have the opportunity to record in, or expensive/rare hardware reverb units. It's also possible to capture an impulse response through a guitar amplifier, from a speaker, microphone or to use any interesting audio file as an impulse response to create weird effects. The process of making impulse responses is discussed in the section 'Making your own impulses' at the bottom of this page.

Alternatives to Fruity Convolver include Fruity Reeverb and Fruity Reeverb 2.

See the Fruity Convolver Video Tutorial Series here.

NOTE: Any audio file can serve as an impulse, experimentation will reward you with unique and interesting sounds.

Options

There are two main areas on the plugin interface. The knobs along the top of the plugin give access to commonly used controls and the lower 'Editor' window that can be switched between impulse, the impulse can be manipulated like any recorded audio, and equalizer that can apply equalization to the impulse.

Impulse

Impulse Editor Window

Fruity Convolver's Impulse Editor is based on Edison, so see Edison's help for features not covered here. The main controls and options needed to use Fruity Convolver's Impulse Editor are:

Impulse Equalizer Window

The equalizer functions acts on the impulse itself, not directly on the audio passing through the plugin, so the effect is to change the EQ of the convolved part of the output. You can also use this section to perform Linear phase EQ (see below). The background display shows a frequency spectrograph with time on the vertical axis (time zero is at the top) and frequency on the horizontal axis (frequency is indicated in Hz and Octaves along the bottom of the display). The EQ can be useful to fine-tune impulse responses that don't have the desired tonal characteristics. Pops & claps often excite the mid-range frequencies more strongly than the low and high frequencies. A gentle U shaped curve can help restore a more pleasing frequency balance.

NOTE: The EQ curve above was created by drawing a rough 6-segment set of straight lines and then applying the Smooth up tool.

Working with the EQ envelope

EQ envelope menu

Linear Phase EQ presets

There are two special presets that turn Fruity Convolver into a Linear Phase Equalizer. That is the phase response of the filter is linear as a function of frequency. Some people claim linear phase filters sound better than other filter types, 'minimum-phase' designs as used in analog EQ and most plugins, particularly on transients. NOTE: The penalty for Linear Phase EQ is a longer plugin latency so PDC may be required for use on all but the Master track.

Use Load a Linear phase EQ preset and set the equalizer curve as discussed in the section above. This process relies on an impulse response that has been centered in the impulse window to allow for a symmetrical impulse response necessary to preserve phase.

Impulse Resources

Fruity Convolver comes with a collection of impulse responses, however the addictive nature of these files will mean that you will soon be looking for more. Below are several links to get you started. To load a new impulse response from outside FL Studio, Left-click on the 'Load File' icon on the Impulse Editor window and browse to the location of the new impulse responses.

Making impulse responses from plugin effects

Making your own impulse responses from plugin effects is fairly simple. Typical candidates are reverb plugins or any effect that does not change as a function of time (e.g. reverb and EQ). Phasing, flanging and delays won't work.

  1. Select a Mixer track and Load Fruity Convolver in FX slot 1 then deactivate it. This Fruity Convolver will be used to create the impulse.
  2. Load the FX plugin to be 'impulsed' in FX slot 2, below the first Fruity Convolver, and set the plugin to the patch/sound you want. Make sure it's passing the Dry input sound also (don't use 100% wet).
  3. Reactivate the Fruity Convolver on FX slot 1.
  4. Load a second Fruity Convolver in FX slot 3. This will be used to record the impulse response from the plugin above.
  5. Click the Record button of Fruity Convolver on FX slot 3. This will arm it for recording.
  6. Click the Trigger impulse (spark icon) of Fruity Convolver on FX slot 1. This will initiate the recording through the plugin on FX slot 2 and into the Fruity Convolver on FX slot 3.
  7. Deactivate the plugins on slots 1 and 2. Test your impulse sounds the same as the FX plugin in slot 2.

Making your own impulses from external sources

This section assumes that you want to make impulse responses of real-world objects, equipment or spaces. If you are interested in making impulse responses from plugins see the 'Trigger impulse' 4-step tutorial in the Impulse Editor Window section above. NOTE: The limitations discussed below don't apply to making impulses from plugins internally in FL Studio.

Making acoustic impulse responses is no more than a specialized exercise in stereo audio recording. If you are capturing reverberation then the quality of the impulse response will depend on the quality of the audio source, the microphones used, the microphone placement, background noises (although sine-wave sweeps avoid this, see below) preamplifier quality and recording equipment. Ideally the recording chain needs to be as transparent as possible so it imparts as little of its own sonic character on the recorded impulse responses. Remember that this process is all about capturing subtle, often low level signals. To do this right you need to have a professional and quality audio recording setup. But this isn't the Image-Line school of scary, 'do it perfectly or don't bother' impulse response recording, we just want to keep your expectations in perspective. If your mobile phone can record audio, why not give it a bash with that, you will still gain insight into the process and your impulse responses will be interesting, if not good.

To create an impulse response you need to record the object being excited by a full audible spectrum (20 Hz to 20 kHz) impulse. There are two main methods for achieving broad-band impulse response recordings:

  1. Noise burst method - The ideal burst sound is a loud, single-cycle wavefront with an infinitely fast pressure-rise, a single spike in air pressure. While it is not practically possible to create a perfect acoustic spike, short, sharp sounds such as hand-claps, two blocks of wood slapped together, loud clicks or white noise blips from good speakers, balloon-pops or starters-guns can substitute reasonably well. This impulse will sound different depending on whether it's heard in a bathroom or a cathedral. Recorded on a mobile telephone or with a $10,000 microphone. These different sounds represent the 'acoustic fingerprint' or echo of the impulse in or through the object. The impulse response therefore captures an acoustic fingerprint and allows us to apply it to any other audio.

    Problems with the noise burst approach include the sonic character of the impulse sound contaminating the impulse response, poor frequency coverage and poor signal to noise ratio as background noises contaminate the recording, particularly the decaying tail.

  2. Sine-wave sweep method - This is the preferred as it avoids many of the problems associated with the noise burst approach. Here we record a sine-wave frequency sweep (20 Hz to 20 kHz) as it excites the acoustic object. After some additional mathematical processing an impulse can be computed from the recording that represents only the sonic characteristics of the object across the frequency spectrum and with a very high signal to noise ratio. In addition to the recording rig you will need a good speaker (possibly amplifier) and CD, portable media player or laptop to play the sine-sweep wav file. Remember we are after quality audio reproduction here.

Impulses can be taken from literally anything that can transmit or reflect audio signals. In addition to sampling reverberation, you can create an impulse from a microphone, e.g. recording a frequency sweep through a Neumann U87 microphone would theoretically capture the 'fingerprint' U87 sound. Similarly, recording a guitar amplifier and cabinet would capture the sound of the electronics and speaker. The applications of impulses is therefore almost unlimited.

Credits

Convolution engine by: LiquidSonics.

Delphi code translation: Frederic Vanmol (reflex).

GUI and Code by: Didier Dambrin (gol).