McDSP’s Revolver convolution reverb plug-in has taken the capabilities of convolution to new heights by providing a multitude of other processing options to further enhance the sound of the reverb itself. Delay lines, routable EQ, reverb contour controls, and stereo field adjustments, features previously only available on ultra high-end synthetic reverbs, are now available in a convolution reverb.

Revovler also comes with tools for creating customized impulse responses for use with the Revolver plug-in. This issue covers the basics of how to import existing impulse responses and create your own impulse responses using the impulse response tools provided with the Revolver convolution reverb plug-in. We’ve even included a set of new impulse responses for Revolver recorded at Fantasy Studios with the assistance of chief engineer Stephen Hart.

Loading Existing Impulse Responses

Revolver comes with hundreds of impulse responses, as well as presets for a variety of applications. The presets always contain the original impulse response (IR) data, unless a new preset is loaded that contains another IR sample. This allows users to make many versions of the original IR preset, while ensuring all needed IR data is stored with the preset, and/or Pro Tools session. In order to minimize the amount of hard drive space used by each Revolver preset, the IR data is compressed before writing to disk.

In order to load impulse responses not provided by McDSP, follow these steps:

• Bring up the McDSP IR Reader AudioSuite plug-in. Note mono or stereo versions of the IR Reader plug-in are available.
• Import the impulse response audio file into the Pro Tools session, and then place it on a track.
• Highlight the audio and press the Analyze button in the Pro Tools toolbar just beneath the IR Reader user interface.

Once the process in completed, the impulse response will be displayed in the IR Reader impulse response plot. The IR Reader plug-in takes the selected audio exactly as presented, so there are several things you may want to address before importing the audio. You should normalize the audio such that the maximum value is 0dB, the end of the sample can be faded out if desired, and the start of the selected audio region should be as close to the beginning of the sample as possible.

Once the new impulse response is calculated, the user can save the impulse response. Note the IR Reader plug-in generates impulse response only presets, so you may want to follow our convention of naming them with the prefix “IR_” when saving the preset in the Revolver settings folder. Finally, the IR preset must be imported into the Revolver plug-in settings folder. Bring up an instance of Revolver then go to the PRESET drop down menu and select IMPORT SETTINGS and navigate to the SWEEP ANALYZER folder where the IR was saved and select it. Once it has been imported it into Revolver only the impulse response data and the image will be updated and the other Revolver settings will be left at their current values. Presets that do not have the prefix “IR_” will change settings other than the IR and image. You now have a new impulse response for your Revolver IR library.

There are many web sites and other sources for new and different impulse response libraries. Some of these impulse responses are licensed, and some are not. Be sure to check with the impulse response provider if you are unsure as to the license agreement that may exist for certain impulse responses.

Creating New Impulse Responses

Revolver comes with a set of tools for sweeping acoustic spaces or outboard equipment and turning the processed sweeps into impulse responses for use with the Revolver plug-in. For a detailed example of how to capture impulse responses, refer to the example session and tutorial included in the Impulse Response Library CDROM included with Revolver.

Load the session entitled ‘Capture Example Session’ from the Revolver Presets Vol1 folder created by the installer. This session contains both mono and stereo sends to which an acoustic environment or outboard device can be connected. Now perform the following steps:

• Select one of the two sets of 30 second sweeps (mono or stereo) using the hand tool. It is important that both the sweep and the recorded response are exactly the same length and are time aligned with each other. Note the Sweep Generator plug-in can also re-generate these sweep signals if they are erased accidentally or if you prefer to create your own session.
• Connect the outboard equipment into the IO inputs and outputs such that the processed sweep is returned to the session. For acoustic environments, the output is routed to speakers, and microphones, placed at strategic locations in the sampled space, are routed back into the session. See the next section for tips and tricks on recording impulses.
• Record-enable the track the processed sweep is routed back into.
• Press play and record the processed sweep.
• Pull up the Sweep Analyzer Audiosuite plug-in. Note mono or stereo versions of the Sweep Analyzer plug-in are available. Both the sweep and response signals must contain the same number of channels.
• Highlight the original sweep using the hand tool, select the ‘Analyze Sweep’ button, and click analyze.
  Highlight the processed sweep using the hand tool, select the ‘Analyze Response’ button, and click analyze. Note this process may take 3 to 5 minutes depending on CPU speed.
• Save the newly created impulse response.

The preset is an ‘impulse only’ setting – it contains only the impulse response data, and no other reverb parameter settings. When ‘impulse only’ settings are selected in the Revolver plug-in, only the impulse response data is updated – all other parameters remain unaffected. McDSP ‘impulse only’ presets are saved with a naming convention of “IR_xxx” as the preset name, so it is a good idea to adopt this naming convention to distinguish regular Revolver presets from ‘impulse only’ presets.

Finally, the IR preset must be imported into the Revolver plug-in settings folder. Bring up an instance of Revolver then go to the PRESET drop down menu and select IMPORT SETTINGS and navigate to the SWEEP ANALYZER folder where the IR was saved and select it. Once it has been imported it into Revolver only the impulse response data and the image will be updated and the other Revolver settings will be left at their current values. Presets that do not have the prefix “IR_” will change settings other than the IR and image. You now have a new impulse response for your Revolver IR library.

This session and tutorial on how to capture impulse responses is included in the Revolver Impulse Response Library CDROM that comes with the Revolver plug-in.

Impulse Response Creation From Other Sounds

Sometimes there is no impulse response from an environment available, but the sound of that space is desired for further audio processing. Typically there is some new audio content being added to a scene, and the goal is to make new audio sound as if it was recorded at the original location.

Other sounds, such as handclaps, ‘scene clappers’, or starter pistol shot, can be used as the impulse response source data.

In order to load in impulse responses not provided by McDSP, follow these steps:

• Bring up the McDSP IR Reader AudioSuite plug-in. Note mono or stereo versions of the IR Reader plug-in are available.
• Import the audio into the Pro Tools session, and then place it on a track. The idea is to treat the audio – be it handclaps, a ‘scene clapper’, or starter pistol shot, as the actual impulse response.
• Highlight the audio and press the Analyze button in the Pro Tools toolbar just beneath the IR Reader user interface. Once the process in completed, the impulse response will be displayed in the IR Reader impulse response plot.
• Once the new impulse response is calculated, the user can save the impulse response.

Note the IR Reader plug-in generates impulse response only presets, you may want to follow our convention of naming them with the prefix “IR_” when saving the preset in of the Revolver settings folder.

Impulse Response Creation Tips

Always strive to get as strong a signal as possible going into the outboard gear or acoustic space. This will improve the signal to noise ratio of the impulse response. Be sure to avoid clipping in any part of the signal path.

While hand claps and starter pistol derived impulses sometime provide adequate samples, using the provided sweep generation and analysis will generate superior results. This is due to the fact that all audible frequencies are excited by the sweep and much more energy is provided to the system. When the system is completely stable and time-invariant (no controls are changing on the outboard gear, and no train is going by, the mics are not moving), the long sweep will provide better results.

When shooting a space or device multiple times, give it plenty of time to settle down. If a previous sound is still reverberating when a new sweep is started, the resulting impulse response will contain the end of the old sweep and the new sweep.

When shooting digital reverbs, try to disable all chorusing effects if possible.

Strategic locations in acoustic spaces are found by using your ears and the space between them. Stand in the room and find ‘good’ sounding places. Just like placing overhead mics near a drum kit in the studio! Actually capturing the sound of the overhead mic position is a great reason to create your own impulse response!