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# Compressor Stages

Compressor Stages allow for control of the dynamic range of the signal, such as reducing the level of loud sounds.

## CompressorRMS

class audio_dsp.stages.CompressorRMS(**kwargs)

  A compressor based on the RMS envelope of the input signal.

  When the RMS envelope of the signal exceeds the threshold, the signal amplitude is reduced by the compression ratio.

  The threshold sets the value above which compression occurs. The ratio sets how much the signal is compressed. A ratio of 1 results in no compression, while a ratio of infinity results in the same behaviour as a limiter. The attack time sets how fast the compressor starts compressing. The release time sets how long the signal takes to ramp up to its original level after the envelope is below the threshold.

  Attributes:
    dsp_block `audio_dsp.dsp.drc.drc.compressor_rms`

      The DSB block class; see RMS Compressor for implementation details.

  make_compressor_rms(
    ratio,
    threshold_db,
    attack_t,
    release_t,
    Q_sig=27,
  )

    Update compressor configuration based on new parameters.

    Parameters:
      ratio float

        Compression gain ratio applied when the signal is above the threshold.

      threshold_db float

        Threshold in decibels above which compression occurs.

      attack_t float

        Attack time of the compressor in seconds.

      release_t float

        Release time of the compressor in seconds.

  set_parameters(
    parameters: CompressorParameters,
  )

    Update compressor parameters.

    Parameters:
      parameters CompressorParameters

        The new parameters to apply to the compressor.

pydantic model audio_dsp.models.compressor.CompressorParameters

  Parameters for compressor stage.

  field attack_t: float = 0.01

    Time in seconds for compressor to start compressing

    Constraints:

      - gt = 0

      - le = 1

  field ratio: float = 4.0

    Compression ratio applied when detect signal exceeds threshold

    Constraints:

      - gt = 1

      - le = 100

  field release_t: float = 0.2

    Time in seconds for signal to return to original level

    Constraints:

      - gt = 0

      - le = 5

  field threshold_db: float = 0.0

    Level in dB above which compression occurs

    Constraints:

      - ge = -81.27809882927492

      - le = 12.041199858916709

### CompressorRMS Control

The following runtime command ids are available for the CompressorRMS Stage. For details on reading and writing these commands, see the Run-Time Control User Guide.

Control parameter | Payload length
--- | ---
CMD_COMPRESSOR_RMS_ATTACK_ALPHA | `sizeof(int32_t)`
The attack alpha in Q0.31 format. To convert an attack time in seconds to an `int32_t` control value, use the function `calc_alpha()` in `control/helpers.h`. |
CMD_COMPRESSOR_RMS_RELEASE_ALPHA | `sizeof(int32_t)`
The release alpha in Q0.31 format. To convert a release time in seconds to an `int32_t` control value, use the function `calc_alpha()` in `control/helpers.h`. |
CMD_COMPRESSOR_RMS_ENVELOPE | `sizeof(int32_t)`
The current RMS² envelope of the signal in Q_SIG format. To read the `int32_t` control value, use the function `qxx_to_db_pow()` in `control/helpers.h` with Q=Q_SIG. This command is read only. When sending a write control command, it will be ignored. |
CMD_COMPRESSOR_RMS_THRESHOLD | `sizeof(int32_t)`
The threshold in Q_SIG format above which compression will occur. To convert a threshold in dB to the `int32_t` control value, use the function `calculate_rms_threshold()` in `control/helpers.h`. |
CMD_COMPRESSOR_RMS_GAIN | `sizeof(int32_t)`
The current gain applied by the compressor in Q0.31 format. To read the `int32_t` control value, use the function `qxx_to_db()` in `control/helpers.h` with Q=31. This command is read only. When sending a write control command, it will be ignored. |
CMD_COMPRESSOR_RMS_SLOPE | `sizeof(float)`
The compression slope of the compressor. This is calculated as `(1 - 1 / ratio) / 2.0`. To convert a ratio to a slope, use the function `rms_compressor_slope_from_ratio()` in `control/helpers.h`. |