Limiter filter. More...
#import <AELimiter.h>
Inherits <NSObject>.
Instance Methods | |
| (id) | - initWithNumberOfChannels:sampleRate: |
| Init. | |
| (BOOL) | - AELimiterEnqueue |
| Enqueue audio. | |
| (void) | - AELimiterDequeue |
| Dequeue audio. | |
| (UInt32) | - AELimiterFillCount |
| Query the fill count of the limiter. | |
| (void) | - AELimiterDrain |
| Dequeue all audio from the limiter, including those held back for the lookahead algorithm. | |
| (void) | - AELimiterReset |
| Reset the buffer, clearing all enqueued audio. | |
Properties | |
| UInt32 | hold |
| The hold interval, in frames. | |
| UInt32 | attack |
| The attack duration, in frames. | |
| UInt32 | decay |
| The decay duration, in frames. | |
| float | level |
| The audio level limit. | |
Detailed Description
Limiter filter.
This class implements a lookahead audio limiter. Use it to smoothly limit output volume to a particular level.
The audio is delayed by the number of frames indicated by the attack property.
This class operates on non-interleaved floating point audio, as it is frequently used as part of larger audio processing operations. If your audio is not already in this format, you may wish to use it in conjunction with AEFloatConverter.
To use this as an AEAudioFilter, see the AELimiterFilter class.
Method Documentation
| - (id) initWithNumberOfChannels: | (int) | numberOfChannels | |
| sampleRate: | (Float32) | sampleRate | |
Init.
- Parameters
-
numberOfChannels Number of channels to use sampleRate Sample rate to use
| - (BOOL) AELimiterEnqueue | (AELimiter *) | limiter | |
| (float **) | buffers | ||
| (UInt32) | length | ||
| (const AudioTimeStamp *) | timestamp | ||
Enqueue audio.
Add audio to be processed.
This C function is safe to be used in a Core Audio realtime thread.
- Parameters
-
limiter A pointer to the limiter object. buffers An array of floating-point arrays containing noninterleaved audio to enqueue. length The length of the audio, in frames timestamp The timestamp of the audio, or NULL
- Returns
- YES on success, NO on failure.
| - (void) AELimiterDequeue | (AELimiter *) | limiter | |
| (float **) | buffers | ||
| (UInt32 *) | ioLength | ||
| (AudioTimeStamp *) | timestamp | ||
Dequeue audio.
Dequeue processed audio.
Note that the audio is delayed by the number of frames indicated by the attack property. If at the end of a processing operation you wish to dequeue all audio from the limiter, you should use AELimiterDrain.
This C function is safe to be used in a Core Audio realtime thread.
- Parameters
-
limiter A pointer to the limiter object. buffers An array of floating-point arrays to store the dequeued noninterleaved audio. ioLength On input, the length of the audio to dequeue, in frames; on output, the amount of audio dequeued. timestamp On output, the timestamp of the next audio, if not NULL.
| - (UInt32) AELimiterFillCount | (AELimiter *) | limiter | |
| (AudioTimeStamp *) | timestamp | ||
| (UInt32 *) | trueFillCount | ||
Query the fill count of the limiter.
Use this to determine how many frames can be dequeued.
- Parameters
-
limiter A pointer to the limiter object. timestamp On output, if not NULL, the timestamp of the next audio frames trueFillCount On output, if not NULL, the true fill count, including the attack frames held back for the lookahead algorithm.
- Returns
- The number of frames that can be dequeued
| - (void) AELimiterDrain | (AELimiter *) | limiter | |
| (float **) | buffers | ||
| (UInt32 *) | ioLength | ||
| (AudioTimeStamp *) | timestamp | ||
Dequeue all audio from the limiter, including those held back for the lookahead algorithm.
During normal operation, the nmuber of frames given by the attack property are held back for the lookahead algorithm to function correctly. If you wish to finish audio processing and want to recover these frames, then you can use this function to do so. Note that the final frames may surpass the set level.
- Parameters
-
limiter A pointer to the limiter object. buffers An array of floating-point arrays to store the dequeued noninterleaved audio. ioLength On input, the length of the audio to dequeue, in frames; on output, the amount of audio dequeued. timestamp On output, the timestamp of the next audio, if not NULL.
| - (void) AELimiterReset | (AELimiter *) | limiter |
Reset the buffer, clearing all enqueued audio.
- Parameters
-
limiter The limiter object.
Property Documentation
|
readwritenonatomicassign |
The hold interval, in frames.
This is the length of time the limiter will hold the gain, when it is in the active state.
Default: 22050 (0.5s at 44.1kHz)
|
readwritenonatomicassign |
The attack duration, in frames.
This is the amount of time over which the limiter will smoothly activate when an audio level greater than the set limit is seen.
Note that the limiter will delay the audio by this duration.
Default: 2048 frames (~.046s at 44.1kHz)
|
readwritenonatomicassign |
The decay duration, in frames.
This is the amount of time over which the limiter will smoothly deactivate, moving back to a 1.0 gain level, once the hold time expires.
Default: 44100 (1s at 44.1kHz)
|
readwritenonatomicassign |
The audio level limit.
This is the audio level at which the limiter activates. The dequeued audio will not exceed this level, and will be smoothly gain-adjusted accordingly when a greater level is seen.
The value you provide here will depend on the original audio format you are working with. For example, if you are mixing a number of 16-bit signed integer streams, you may wish to use a limit value of INT16_MAX for the combined stream before converting back to 16-bit, to avoid clipping.
Default: INT16_MAX
The documentation for this class was generated from the following file: