# Multichannel biquadratic filters Filter a multichannel signal with a cascade of biquadratic sections. ## Discussion The vDSP library implements biquadratic filtering as a cascade of individual infinite impulse response (IIR) filters called *sections.* Each section has its own set of feedback and feedforward coefficients, and implements a direct-form 2 filter. When the biquadratic filter function executes, the sections execute in sequence. Each section processes the entire input signal and passes its output to the next section for further processing. > Note: > The vDSP biquadratic filters work in place. That is, the source and destination pointers may point to the same memory. > Note on performance and energy efficiency: > Although you can use to process a single channel of data, it’s optimized for processing multiple channels of data independently. When processing only a single channel, the single-channel API ``doc://com.apple.accelerate/documentation/Accelerate/vDSP_biquad`` may provide better performance and energy efficiency. When processing a single channel in isolation, it’s best practice to use ``doc://com.apple.accelerate/documentation/Accelerate/vDSP_biquad`` whenever possible. ## Topics ### Equalizing audio with biquadratic filters ### Creating a multichannel biquadratic filter setup [`extern vDSP_biquadm_SetupvDSP_biquadm_CreateSetup(const double *__coeffs, vDSP_Length __M, vDSP_Length __N);`](/documentation/Accelerate/vDSP_biquadm_CreateSetup) Builds a data structure that contains precalculated data for use by a single-precision, multichannel cascaded biquadratic filter function. [`typealias vDSP_biquadm_Setup`](/documentation/Accelerate/vDSP_biquadm_Setup) A data structure that contains precalculated data for use by a single-precision, multichannel cascaded biquadratic filter function. [`extern vDSP_biquadm_SetupDvDSP_biquadm_CreateSetupD(const double *__coeffs, vDSP_Length __M, vDSP_Length __N);`](/documentation/Accelerate/vDSP_biquadm_CreateSetupD) Builds a data structure that contains precalculated data for use by a double-precision, multichannel cascaded biquadratic filter function. [`typealias vDSP_biquadm_SetupD`](/documentation/Accelerate/vDSP_biquadm_SetupD) A data structure that contains precalculated data for use by a double-precision, multichannel cascaded biquadratic filter function. ### Copying the filter state of a multichannel biquadratic filter [`extern void vDSP_biquadm_CopyState(vDSP_biquadm_Setup __dest, const struct vDSP_biquadm_SetupStruct *__src);`](/documentation/Accelerate/vDSP_biquadm_CopyState) Copies the filter state from one single-precision multichannel biquadratic IIR filter object to another. [`extern void vDSP_biquadm_CopyStateD(vDSP_biquadm_SetupD __dest, const struct vDSP_biquadm_SetupStructD *__src);`](/documentation/Accelerate/vDSP_biquadm_CopyStateD) Copies the filter state from one double-precision multichannel biquadratic IIR filter object to another. ### Resetting the filter state of a multichannel biquadratic filter [`extern void vDSP_biquadm_ResetState(vDSP_biquadm_Setup __setup);`](/documentation/Accelerate/vDSP_biquadm_ResetState) Resets the filter state of a single-precision multichannel biquadratic IIR filter object. [`extern void vDSP_biquadm_ResetStateD(vDSP_biquadm_SetupD __setup);`](/documentation/Accelerate/vDSP_biquadm_ResetStateD) Resets the filter state of a double-precision multichannel biquadratic IIR filter object. ### Setting the filter state of a multichannel biquadratic filter [`extern void vDSP_biquadm_SetActiveFilters(vDSP_biquadm_Setup __setup, const _Bool *__filter_states);`](/documentation/Accelerate/vDSP_biquadm_SetActiveFilters) Activates or deactivates individual sections in a single-precision, multichannel biquadratic filter. [`extern void vDSP_biquadm_SetActiveFiltersD(vDSP_biquadm_SetupD __setup, const _Bool *__filter_states);`](/documentation/Accelerate/vDSP_biquadm_SetActiveFiltersD) Activates or deactivates individual sections in a double-precision, multichannel biquadratic filter. ### Setting the coefficients of a multichannel biquadratic filter [`extern void vDSP_biquadm_SetCoefficientsSingle(vDSP_biquadm_Setup __setup, const float *__coeffs, vDSP_Length __start_sec, vDSP_Length __start_chn, vDSP_Length __nsec, vDSP_Length __nchn);`](/documentation/Accelerate/vDSP_biquadm_SetCoefficientsSingle) Sets the single-precision coefficients of the specified single-precision, multichannel biquadratic filter setup object. [`extern void vDSP_biquadm_SetCoefficientsDouble(vDSP_biquadm_Setup __setup, const double *__coeffs, vDSP_Length __start_sec, vDSP_Length __start_chn, vDSP_Length __nsec, vDSP_Length __nchn);`](/documentation/Accelerate/vDSP_biquadm_SetCoefficientsDouble) Sets the double-precision coefficients of the specified single-precision, multichannel biquadratic filter setup object. [`extern void vDSP_biquadm_SetCoefficientsSingleD(vDSP_biquadm_SetupD __setup, const float *__coeffs, vDSP_Length __start_sec, vDSP_Length __start_chn, vDSP_Length __nsec, vDSP_Length __nchn);`](/documentation/Accelerate/vDSP_biquadm_SetCoefficientsSingleD) Sets the single-precision coefficients of the specified double-precision, multichannel biquadratic filter setup object. [`extern void vDSP_biquadm_SetCoefficientsDoubleD(vDSP_biquadm_SetupD __setup, const double *__coeffs, vDSP_Length __start_sec, vDSP_Length __start_chn, vDSP_Length __nsec, vDSP_Length __nchn);`](/documentation/Accelerate/vDSP_biquadm_SetCoefficientsDoubleD) Sets the double-precision coefficients of the specified double-precision, multichannel biquadratic filter setup object. ### Setting the target values of a multichannel biquadratic filter [`extern void vDSP_biquadm_SetTargetsSingle(vDSP_biquadm_Setup __setup, const float *__targets, float __interp_rate, float __interp_threshold, vDSP_Length __start_sec, vDSP_Length __start_chn, vDSP_Length __nsec, vDSP_Length __nchn);`](/documentation/Accelerate/vDSP_biquadm_SetTargetsSingle) Sets the single-precision coefficient target values of the specified single-precision, multichannel biquadratic filter setup object. [`extern void vDSP_biquadm_SetTargetsDouble(vDSP_biquadm_Setup __setup, const double *__targets, float __interp_rate, float __interp_threshold, vDSP_Length __start_sec, vDSP_Length __start_chn, vDSP_Length __nsec, vDSP_Length __nchn);`](/documentation/Accelerate/vDSP_biquadm_SetTargetsDouble) Sets the double-precision coefficient target values of the specified single-precision, multichannel biquadratic filter setup object. [`extern void vDSP_biquadm_SetTargetsSingleD(vDSP_biquadm_SetupD __setup, const float *__targets, double __interp_rate, double __interp_threshold, vDSP_Length __start_sec, vDSP_Length __start_chn, vDSP_Length __nsec, vDSP_Length __nchn);`](/documentation/Accelerate/vDSP_biquadm_SetTargetsSingleD) Sets the single-precision coefficient target values of the specified double-precision, multichannel biquadratic filter setup object. [`extern void vDSP_biquadm_SetTargetsDoubleD(vDSP_biquadm_SetupD __setup, const double *__targets, double __interp_rate, double __interp_threshold, vDSP_Length __start_sec, vDSP_Length __start_chn, vDSP_Length __nsec, vDSP_Length __nchn);`](/documentation/Accelerate/vDSP_biquadm_SetTargetsDoubleD) Sets the double-precision coefficient target values of the specified double-precision, multichannel biquadratic filter setup object. ### Applying a multichannel biquadratic filter [`extern void vDSP_biquadm(vDSP_biquadm_Setup __Setup, const float **__X, vDSP_Stride __IX, float **__Y, vDSP_Stride __IY, vDSP_Length __N);`](/documentation/Accelerate/vDSP_biquadm) Applies a single-precision multichannel biquadratic IIR filter. [`extern void vDSP_biquadmD(vDSP_biquadm_SetupD __Setup, const double **__X, vDSP_Stride __IX, double **__Y, vDSP_Stride __IY, vDSP_Length __N);`](/documentation/Accelerate/vDSP_biquadmD) Applies a double-precision multichannel biquadratic IIR filter. ### Destroying a multichannel biquadratic filter setup [`extern void vDSP_biquadm_DestroySetup(vDSP_biquadm_Setup __setup);`](/documentation/Accelerate/vDSP_biquadm_DestroySetup) Destroys a single-precision multichannel biquadratic filter setup object. [`extern void vDSP_biquadm_DestroySetupD(vDSP_biquadm_SetupD __setup);`](/documentation/Accelerate/vDSP_biquadm_DestroySetupD) Destroys a double-precision multichannel biquadratic filter setup object. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)