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Using convolution correctly

From: Foundations of Audio: Reverb

Video: Using convolution correctly

Convolution brings a major capability to our studio. Any track we record using typical close miking techniques can be sonically transported to sound as if it were recorded in any space in the world. All you need is the impulse response of that space. We use convolution to put our pianos in the finest concert halls in Europe, our drums in the best recording studios in Los Angeles, and our vocals in the most thunderously awesome caves in Africa. But convolution does have limits, so we take a look under the hood in this movie and the next, so that we're better informed users of the technology.

Using convolution correctly

Convolution brings a major capability to our studio. Any track we record using typical close miking techniques can be sonically transported to sound as if it were recorded in any space in the world. All you need is the impulse response of that space. We use convolution to put our pianos in the finest concert halls in Europe, our drums in the best recording studios in Los Angeles, and our vocals in the most thunderously awesome caves in Africa. But convolution does have limits, so we take a look under the hood in this movie and the next, so that we're better informed users of the technology.

Recall the convolution is done by sending an impulse into the room, a simple single instantaneous spike and recording the resulting pattern of spikes that follows. This pattern of spikes defines the sound of the room. It's called the impulse response, as it is the acoustic response of the room to an impulse signal. The process of convolution applies the room's response to any other signal we feed it. But the process doesn't work for things that change over time. Imagine a room where the walls move. Such spaces are very rare, but it illustrates a critical point.

If the walls move, then the pattern of spikes that make up the impulse response will change too. But convolution only has the ability to apply a fixed impulse response to your audio. So a system that changes simply can't be re-created through convolution. Fair enough, the spaces I care about don't change much. The walls don't move in most symphony halls, cathedrals, and famous reverb chambers. Convolution is great for these spaces. What about springs and plates? They too don't change the resident behavior during the course of a mix, so convolution is a terrific way to bring vintage springs and plates into your productions.

You'll also see convolution use to simulate other algorithmic digital reverbs. This usually doesn't work. The oldest digital reverbs ran simpler static algorithms that can be represented by fixed impulse response. But the high-end algorithmic reverbs since the 90s pretty much always use changing delays within their algorithm. So convolution can't convey the full rich complexity of their sound. To use convolution where appropriate, make sure that the space or device it is stimulating exhibits steady behavior.

It's ideal for reproducing the sounds of springs, plates, and every glorious space you want to hear in your mixes.

Show transcript

This video is part of

Image for Foundations of Audio: Reverb
Foundations of Audio: Reverb

39 video lessons · 8183 viewers

Alex U. Case
Author

 
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  1. 9m 41s
    1. Welcome
      1m 58s
    2. What you need to know before watching this course
      2m 18s
    3. Songs you should listen to while watching this course
      2m 46s
    4. Using the exercise files
      55s
    5. Using the Get in the Mix session files
      1m 44s
  2. 6m 44s
    1. What is reverb?
      2m 35s
    2. Why do we use reverb?
      4m 9s
  3. 24m 33s
    1. Capturing reverb acoustically through room tracks
      5m 33s
    2. Creating reverb acoustically through a reverb chamber
      2m 51s
    3. Creating reverb mechanically using springs and plates
      5m 8s
    4. Creating reverb digitally via algorithms and convolution
      4m 51s
    5. Optimizing signal flow, effects loops, and CPU resources
      6m 10s
  4. 39m 10s
    1. The anatomy of reverberation
      3m 8s
    2. Mastering reverb time, predelay, and wet/dry mix parameters
      5m 36s
    3. Understanding the frequency dependence of reverberation
      4m 56s
    4. Tapping into advanced parameters such as diffusion, density, and more
      4m 37s
    5. Reference values from the best orchestra halls
      5m 40s
    6. Hearing beyond the basic parameters
      5m 31s
    7. Touring the interfaces for six reverb plugins
      9m 42s
  5. 1h 32m
    1. Choosing the right reverb for each of your tracks
      2m 17s
    2. Simulating space with reverb
      5m 42s
    3. Hearing space in the mix
      6m 33s
    4. Timbre and texture
      3m 36s
    5. Shaping tone and timbre with reverb
      5m 49s
    6. Creating contrasting sounds for your tracks
      4m 43s
    7. Using nonlinear reverb to help a track cut through
      4m 25s
    8. Emphasizing the reverb using predelay
      3m 24s
    9. Strategically blurring and obscuring tracks
      1m 46s
    10. Get in the Mix: Changing the scene by changing reverb
      7m 37s
    11. Get in the Mix: Gating reverb to emphasize any track in your production
      5m 52s
    12. Reversing reverb to highlight musical moments
      9m 36s
    13. Synthesizing new sounds through reverb
      6m 42s
    14. Get in the Mix: Supporting a track with regenerative reverb
      6m 31s
    15. Getting the most out of room tracks
      17m 39s
  6. 11m 32s
    1. Setting up your own reverb chamber: The architecture
      2m 2s
    2. Setting up your own reverb chamber: The audio
      4m 8s
    3. Using convolution correctly
      2m 32s
    4. Getting great impluse response
      2m 50s
  7. 1m 29s
    1. Next steps
      1m 29s

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