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# AEC #define constants

group aec_defines

  Defines

  AEC_LIB_MAX_Y_CHANNELS

    Maximum number of microphone input channels supported in the library. Microphone input to the AEC refers to the input from the device’s microphones from which AEC removes the echo created in the room by the device’s loudspeakers.

    AEC functions follow the convention of using \(y\) and \(Y\) for referring to time domain and frequency domain representation of microphone input.

    The `num_y_channels` passed into aec_init() call should be less than or equal to AEC_LIB_MAX_Y_CHANNELS. This define is only used for defining data structures in the aec_state. The library code implementation uses only the num_y_channels aec is initialised for in the aec_init() call.

  AEC_LIB_MAX_X_CHANNELS

    Maximum number of reference input channels supported in the library. Reference input to the AEC refers to a copy of the device’s speaker output audio that is also sent as an input to the AEC. It is used to model the echo characteristics between a mic-loudspeaker pair.

    AEC functions follow the convention of using \(x\) and \(X\) for referring to time domain and frequency domain representation of reference input.

    The `num_x_channels` passed into aec_init() call should be less than or equal to AEC_LIB_MAX_X_CHANNELS. This define is only used for defining data structures in the aec_state. The library code implementation uses only the num_x_channels aec is initialised for in the aec_init() call.

  AEC_FRAME_ADVANCE

    AEC frame size This is the number of samples of new data that the AEC works on every frame. 240 samples at 16kHz is 15msec. Every frame, the echo canceller takes in 15msec of mic and reference data and generates 15msec of echo cancelled output.

  AEC_PROC_FRAME_LENGTH

    Time domain samples block length used internally in AEC’s block LMS algorithm

  AEC_FD_FRAME_LENGTH

    Number of bins of spectrum data computed when doing a DFT of a AEC_PROC_FRAME_LENGTH length time domain vector. The AEC_FD_FRAME_LENGTH spectrum values represent the bins from DC to Nyquist.

  AEC_LIB_MAX_PHASES

    Maximum total number of phases supported in the AEC library This is the maximum number of total phases supported in the AEC library. Total phases are calculated by summing phases across adaptive filters for all x-y pairs.

    For example. for a 2 y-channels, 2 x-channels, 10 phases per x channel configuration, there are 4 adaptive filters, H_haty0x0, H_haty0x1, H_haty1x0 and H_haty1x1, each filter having 10 phases, so the total number of phases is 40. When aec_init() is called to initialise the AEC, the num_y_channels, num_x_channels and num_main_filter_phases parameters passed in should be such that num_y_channels * num_x_channels * num_main_filter_phases is less than equal to AEC_LIB_MAX_PHASES.

    This define is only used when defining data structures within the AEC state structure. The AEC algorithm implementation uses the num_main_filter_phases and num_shadow_filter_phases values that are passed into aec_init().

  AEC_UNUSED_TAPS_PER_PHASE

    Overlap data length

  AEC_FFT_PADDING

    Extra 2 samples you need to allocate in time domain so that the full spectrum (DC to nyquist) can be stored after the in-place FFT. NOT USER MODIFIABLE.