Describe the steps involved in creating a custom reverb impulse response and explain how it can be used to impart unique spatial characteristics to your tracks.
Creating a custom reverb impulse response (IR) allows you to capture the unique acoustic characteristics of a real-world space or even a digitally synthesized environment. An IR is essentially a recording of how a space responds to a short, sharp sound, and when applied to other sounds via convolution reverb, it recreates the spatial qualities of the captured environment. This method allows for unique, realistic and creative reverb effects in your mix.
Steps Involved in Creating a Custom Reverb Impulse Response:
1. Choosing a Space/Environment:
The first step is to select the space or environment you want to capture. This could be anything from a large concert hall to a small bathroom, a hallway, an underground tunnel, or even a synthesized virtual space. The chosen environment will determine the character of the reverb. Consider what kind of sound you are looking for, whether it's a long, lush reverb of a cathedral, or a short, metallic reverb of a trash can, or anything in between. The choice of environment will greatly determine the qualities of the IR.
For example, a stone corridor will create a reverb that is relatively short and with a metallic quality to it, while a large hall will produce a lush, long reverb decay with a much more natural quality to it. The room itself is the initial and most important step of IR capture.
2. Generating the Sweep Signal:
An impulse response requires an input that contains a wide range of frequencies. A sine sweep, which is a signal that sweeps through the audible frequency range, is often used for this purpose. The sine sweep will provide the range of frequencies required for capturing the complete picture of the space's reverb. The sweep signal must be at a suitable volume to be recorded properly, without causing clipping or distortion.
3. Setting Up the Recording Equipment:
Place a microphone in the space where you want to capture the reverberation. The microphone placement affects the character of the reverb: placing the microphone in the center of a room may capture a more balanced sound, while placing it near a wall can result in a more reflective and colored reverb. Choosing the correct microphone will also affect the sound. A high quality microphone with a flat frequency response is ideal for capturing the most accurate impulse response possible. Position the microphone and the sound source so that they capture the essence of the space. Set the microphone gain to a level that is high enough to capture the sweep signal but also ensure that there is no clipping or distortion.
4. Playing and Recording the Sweep Signal:
Play the sine sweep signal from a speaker placed in the space, and simultaneously record the audio using your chosen microphone. Use a high quality audio interface to ensure that the recording is clean and accurate. Ensure the speaker is in the area where the sounds will be generated when a track is actually being mixed. In the recording, you should capture the sweep signal along with the room’s reverberation, creating a recording that will form the basis for the IR.
5. Deconvolution:
The recorded sweep signal needs to be deconvolved to extract the impulse response. Deconvolution is the process of removing the sine sweep signal from the recorded audio, leaving only the impulse response of the space. This step is typically done using dedicated software or plugins, such as a deconvolution plugin in your DAW or a third party software. The deconvolution process is usually done with just one mouse click in most tools, after the recording has been loaded into the tool. The result of deconvolution is the raw IR of the space, ready for use in a convolution reverb plugin.
6. Cleaning and Editing the Impulse Response:
The raw IR may contain unwanted noise or artifacts. Use an audio editor to clean up the signal, removing any unwanted sounds and noise. This may include removing pops and clicks, or background noise that was picked up during the recording process. It might be required to normalize the IR, or trim it to only the specific section needed. For example, if a longer reverb tail is needed, edit the IR so that the tail is properly included. It can also be useful to fade the IR, to avoid any abrupt endings.
7. Saving the Impulse Response:
After the cleanup is completed, save the final IR as a standard WAV file or AIFF file which can then be imported into a convolution reverb plugin. The IR is typically saved in mono, to avoid any potential phase issues. Keep the files organized so they are easy to find for later use in convolution reverbs.
Using the Custom Reverb Impulse Response:
Once you have a custom IR, you can load it into any convolution reverb plugin. A convolution reverb will then process the audio signal through the newly created impulse response, and the output will be processed to sound as if the source was played in the environment that the IR was captured from.
Examples of Use:
1. Realistic Room Reverb: Applying the IR of a specific room, like a concert hall or a small studio, can provide a very realistic sense of space to your instruments and vocals. Using a real space will provide a more realistic and natural feel to the reverb compared to an algorithmic reverb, for example.
2. Unique and Creative Reverb: Using the IR of a unconventional space can give a very creative and unique reverb character to sounds. Imagine the sound of a snare in an abandoned concrete tunnel, or of a vocal track in an underground cave. The possibilities are endless with custom impulse responses.
3. Matching Spaces: If you’ve recorded multiple instruments in different rooms, custom IRs can help match the acoustic characteristics of the spaces together to create a cohesive sound. This can also be used to add a sense of cohesion in an overall mix, where many elements are mixed to sound as though they were in the same environment.
4. Sound Design: By using an IR of a synthesized environment, such as a complex filter or digital effect, you can create unique and often abstract reverb effects that add a lot of depth, texture, and character. You can synthesize a space, then use its IR for completely unique and unconventional reverbs.
In summary, creating a custom reverb impulse response involves carefully recording the sound of a real or synthesized environment and then processing it in order to capture its unique acoustic qualities. By using this, you can then enhance the spatial characteristics of your tracks with detailed realism or unique creativity. This makes custom IRs a very powerful and versatile tool for hip hop mixing and production.