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Digital Audio Principles

Dynamics pt. 1: Compressors, limiters, expanders, and gates


From:

Digital Audio Principles

with Dave Schroeder

Video: Dynamics pt. 1: Compressors, limiters, expanders, and gates

Now let's take a look at plug- ins that deal with dynamics; that means plug-ins that affect the dynamic range of a sound. Now, these effects work kind of based on the relationship of a sound to a threshold. A threshold is a certain level of volume that you set that once the sound interacts with it, the Dynamics plug-in is going to do something to that sound. There are basically two kinds of effects in the dynamics processing world. There are those that care about any sound that goes above the threshold, and then there are those that care about what sounds don't make it up to the threshold, or live below the threshold.
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  1. 50s
    1. Welcome
      50s
  2. 39m 10s
    1. What is sound?
      4m 15s
    2. Hertz and frequency response
      5m 34s
    3. Phase
      2m 39s
    4. Capturing audio
      3m 39s
    5. Sample rate
      6m 16s
    6. Bit depth
      9m 47s
    7. The waveform
      5m 3s
    8. Audio file formats
      1m 57s
  3. 7m 25s
    1. What is a digital audio workstation?
      2m 59s
    2. Typical DAW signal flow
      4m 26s
  4. 50m 33s
    1. What microphones do
      1m 57s
    2. Element types
      5m 0s
    3. Pickup patterns
      6m 51s
    4. Axis
      2m 52s
    5. Frequency response and the proximity effect
      5m 10s
    6. Phase issues
      1m 41s
    7. Microphone types
      8m 44s
    8. Miking vocals
      5m 39s
    9. Miking amplifiers
      2m 17s
    10. Miking drums
      10m 22s
  5. 16m 39s
    1. Cables and connectors overview
      2m 42s
    2. Balanced and unbalanced cables
      3m 19s
    3. Common cable types
      7m 13s
    4. Cable tips
      3m 25s
  6. 12m 16s
    1. What is an I/O device?
      1m 41s
    2. Analog to digital conversion
      3m 10s
    3. Tour of an audio interface
      4m 49s
    4. Interface considerations
      2m 36s
  7. 21m 5s
    1. What is a preamp?
      3m 21s
    2. Input levels
      5m 29s
    3. Padding
      2m 18s
    4. Phantom power
      2m 37s
    5. Phase reverse
      3m 4s
    6. Preamp demo
      4m 16s
  8. 12m 56s
    1. What is a mixer?
      5m 55s
    2. Input section
      1m 17s
    3. Channel strips
      3m 16s
    4. Master section
      2m 28s
  9. 18m 21s
    1. What is monitoring?
      2m 11s
    2. Speakers
      4m 47s
    3. Room considerations
      5m 43s
    4. Headphone types
      3m 50s
    5. Monitoring levels
      1m 50s
  10. 15m 23s
    1. What role do computers play?
      1m 36s
    2. Performance issues
      4m 11s
    3. Hard drives
      4m 38s
    4. Mechanical noise
      2m 10s
    5. Authorization
      2m 48s
  11. 6m 54s
    1. Planning for recording
      54s
    2. Doing a system check
      1m 26s
    3. Planning your inputs
      1m 42s
    4. The recording environment
      2m 52s
  12. 25m 52s
    1. Types of digital audio software
      38s
    2. Multi-track recorders/sequencers
      4m 56s
    3. Two-track recorders/waveform editors
      4m 55s
    4. Loop-based music production software
      5m 44s
    5. Plug-ins
      6m 56s
    6. Other varieties
      2m 43s
  13. 18m 59s
    1. Common components
      46s
    2. The transport
      2m 4s
    3. The toolbar
      3m 19s
    4. The Edit/Arrange window
      4m 42s
    5. The mixer
      5m 8s
    6. The file list
      3m 0s
  14. 19m 17s
    1. Setting up a session
      3m 30s
    2. Assigning inputs and getting signals
      3m 19s
    3. Input modes
      3m 28s
    4. Overdubbing and punching
      5m 14s
    5. Bouncing down
      3m 46s
  15. 19m 42s
    1. What is editing?
      1m 21s
    2. Waveforms
      2m 53s
    3. Making silent cuts and trims
      7m 1s
    4. Fades and automation
      8m 27s
  16. 1h 23m
    1. What are plug-ins?
      3m 0s
    2. Using plug-ins
      6m 11s
    3. EQs
      7m 4s
    4. Dynamics pt. 1: Compressors, limiters, expanders, and gates
      5m 40s
    5. Dynamics pt 2: Applying dynamic effects
      7m 2s
    6. Pitch shifting
      6m 14s
    7. Reverb
      9m 28s
    8. Echo and delay
      6m 23s
    9. Modulation effects: Phaser, flanger, and chorus
      9m 39s
    10. Sound tools pt. 1: About, gain, normalize
      7m 39s
    11. Sound tools pt. 2: Reverse and time compression/expansion
      6m 29s
    12. Sound tools pt. 3: Noise reducers, dither
      8m 11s
  17. 23m 43s
    1. What is MIDI?
      3m 6s
    2. Keyboard controllers
      1m 23s
    3. Computer-based virtual instruments
      1m 6s
    4. Control surfaces
      1m 6s
    5. Recording and editing MIDI
      12m 4s
    6. Virtual instruments
      4m 58s
  18. 27m 29s
    1. What is mixing?
      1m 54s
    2. Some common objectives
      3m 4s
    3. Some useful techniques
      5m 59s
    4. A quick mixing demo
      16m 32s
  19. 18m 48s
    1. What is mastering?
      2m 24s
    2. Sonic maximization
      9m 43s
    3. Final preparations and exporting
      6m 41s
  20. 13m 34s
    1. What is audio compression?
      2m 16s
    2. Popular formats
      2m 9s
    3. Bit rate, sample rate, and channels
      5m 42s
    4. Other adjustments and considerations
      3m 27s
  21. 15m 6s
    1. Essential gear
      7m 36s
    2. Voice recording setups
      1m 43s
    3. The voice production process
      5m 47s
  22. 10m 4s
    1. Analog vs. digital
      2m 48s
    2. Tube vs. solid state
      5m 6s
    3. The continual upgrade
      2m 10s
  23. 18s
    1. Goodbye
      18s

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Digital Audio Principles
7h 57m Appropriate for all Mar 02, 2007

Viewers: in countries Watching now:

Whether one is producing music, podcasts, game sounds, or film sound effects, Digital Audio Principles provides the tips and techniques that will make the project a success. Author Dave Schroeder explains the basics of digital audio production techniques and covers the essential hardware and software. He also discusses sound theory, frequency response, the range of human hearing, and dynamic range.

Subjects:
Audio + Music Audio Foundations Acoustics Microphones
Author:
Dave Schroeder

Dynamics pt. 1: Compressors, limiters, expanders, and gates

Now let's take a look at plug- ins that deal with dynamics; that means plug-ins that affect the dynamic range of a sound. Now, these effects work kind of based on the relationship of a sound to a threshold. A threshold is a certain level of volume that you set that once the sound interacts with it, the Dynamics plug-in is going to do something to that sound. There are basically two kinds of effects in the dynamics processing world. There are those that care about any sound that goes above the threshold, and then there are those that care about what sounds don't make it up to the threshold, or live below the threshold.

So, let's start by taking a look at those that care about the sounds that go above the threshold. These are known as compressors or limiters. So, a compressor and a limiter are kind of the same animal; they are just different degrees of effect. We'll start by kind of talking about the compressor, and then show you that the limiter is really the same thing, just with one setting slightly different. So, in this graph, I'm representing sounds, volume levels, like in your meters, and I've set a threshold here, and I've decided that this is the threshold.

So, when a sound stays below that threshold, we're not going to have any effect. In all these little two-bar graphs, I have the initial sound, and then this represents what's actually happening, what they compressor does to that sound. So, if a sound doesn't hit the threshold, if it's not loud enough, it gets left alone, and it sounds the way it sounds. If a sound goes beyond the threshold, then what the compressor does is it actually compresses that sound, the volume of that sound, back down. It does it according to a ratio, which I've got up here.

In this situation, we have a 1:1 ratio. So, for every one DB--let's say these lines are different one DB, two DB, three DB--for every one DB we go above the threshold, the compressor is going to turn that sound down by one DB. So we have a 1:1 ratio. In this instance, we have a 2:1, and our sound has gone above at 4 DB. As a result, we're going to push that down two, which means for every two DB it goes above the threshold, push it down by one.

That's your 2:1 ratio. Now, this is really helpful for keeping sounds obviously at a kind of consistent volume. Anything that goes above that threshold, we want to bring it kind of back closer to our threshold, because that's the volume we want to keep things at. This is really useful if you're working on something like a voiceover where there is lots of loud transients. You kind of want to make everything about the same volume, so that when other people listen back to it, they don't have to strain to hear quiet parts, and then there are loud parts. There's a way of kind of leveling things off. Now the limiter is basically the extreme version of that.

It does what it's called. It limits the sound. So, when you set the threshold with a limiter, it doesn't matter how much louder that sound is than the threshold, you're always going to get that sound. Now this seems like, well, why wouldn't we always use that? But the problem is that the way dynamics work is that you're really turning down the volume. It's like if you can imagine sitting there and turning a volume knob really fast. You know what that sounds like, that there's an unevenness, their volume changes, and to the human ear we can hear that. So, a limiter actually, a lot of times when it's used, sounds kind of unnatural, because we know that there is some forceful dynamic changes going on there.

We use a compressor because it's a little bit more of a natural-sounding effect, but you'll use both of them in audio quite a bit. We'll show you a few examples, and I'll show a couple examples in this movie. Next let's look at an image for the expander, or gate. These are the Dynamics plug-ins that are concerned about the sounds below the threshold. Again, we've got the same sort of setup: a threshold, volume, and sounds coming up. But this time, we're interested in sounds below the threshold. Any sound that doesn't make it up to the threshold basically doesn't qualify.

If you can't make it to the threshold, we don't care about you, and we don't want to hear you. So, we assign a ratio to turn things down that are below that threshold. So, in this case, we've got a sound that's not quite loud enough. We've pushed that sound back down. Now, this is useful if you have a track where someone is speaking, but in between when they're speaking, there is a little bit of background noise that's kind of quite, but you wish it was a lot quieter. This can be useful in terms of when the person starts to speak, if we set the threshold so that their voice just breaks the threshold, we'll always hear them speak.

But then when they're done, we'll have the volume of the rest of the background noise pushed back down. So, it allows us to separate the volume difference between what we want to hear and what we don't want to hear. A gate, kind of like the way the limiter is the extreme version of the compressor, the gate is kind of the extreme version of the expander. It's basically an open-and-shut deal. It's like a garage door: either you can pull in or you can't. There's no, well, if you make it, we'll give you a little bit. We've set the threshold, and any sound that doesn't make it over that threshold is squashed, and we don't hear it at all.

So, anything that doesn't make it up to our threshold, we never hear. We'll show you an example of this. It's great for using this on things like drums, or things where you want kind of a real fast open-and-close situation. I should also mention that we're looking at expanders as downward expanders. But there is also a way commonly to set an expander to work as an upward expander in which sounds above the threshold are actually turned up. As opposed to turning down the quiet sounds and moving the noise down, we're taking what we want here, like the voiceover, and making it even louder.

But generally, assuming that you've set your recording levels well and gotten a full signal, you'll probably be using a downward expander most of the time. Now, let's go back into Pro Tools and open a few of these up, and take a look at how they actually work with sound files.

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