The Multirate Filter Analysis VIs can be used to calculate the frequency response of the fixed-point multirate filter and, based on the frequency response results, it can be determined if the fixed-point filter meets the requirements.

Quantization can cause the characteristics of a fixed-point multirate filter to deviate from the reference floating-point multirate filter. Sometimes quantization even causes the resulting fixed-point multirate filter to fail to meet the target specifications. Therefore, after quantization, you must analyze the behavior of the fixed-point multirate filter. If the fixed-point filter does not meet the target specifications, try either or both of the following methods:

  • Modify the quantization settings for the word length of the coefficients.
  • Modify the specifications of the reference floating-point multirate filter to allow larger headroom. A larger headroom helps alleviate fixed-point effects.

To optimize the resulting multirate fixed-point filter, analyze and adjust the filter design iteratively until the frequency response meets the target specifications.