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# maximizestopband

Maximize stopband attenuation of fixed-point filter

## Syntax

```Hq = maximizestopband(Hd,Wordlength) Hq = maximizestopband(Hd,Wordlength,'Ntrials',N) ```

## Description

`Hq = maximizestopband(Hd,Wordlength)` quantizes the single-stage or multistage FIR filter `Hd` and returns the fixed-point filter `Hq` with wordlength `wordlength` that maximizes the stopband attenuation. `Hd` must be generated using `fdesign` and `design`. For multistage filters, `wordlength` can either be a scalar or vector. If `wordlength` is a scalar, the same wordlength is used for all stages. If `wordlength` is a vector, each stage uses the corresponding element in the vector. The vector length must equal the number of stages. `maximizestopband` uses a stochastic noise-shaping procedure by default to minimize the wordlength. To obtain repeatable results on successive function calls, initialize the uniform random number generator `rand`

`Hq = maximizestopband(Hd,Wordlength,'Ntrials',N)` specifies the number of Monte Carlo trials to use in the maximization. `Hq` is the fixed-point filter with the largest stopband attenuation among the trials. The number of Monte Carlo trials `N` defaults to 1.

You must have the Fixed-Point Designer™ software installed to use this function.

## Examples

collapse all

Maximize stopband attenuation for 16-bit fixed-point filter.

```Hf = fdesign.lowpass('Fp,Fst,Ap,Ast',0.4,0.45,0.5,60); Hd = design(Hf,'equiripple'); ```

Use 16 bits to represent coefficients.

```WL = 16; Hq = maximizestopband(Hd,WL); ```

Compare stopband attenuation

```md = measure(Hd) ```
```md = Sample Rate : N/A (normalized frequency) Passband Edge : 0.4 3-dB Point : 0.41178 6-dB Point : 0.41845 Stopband Edge : 0.45 Passband Ripple : 0.49369 dB Stopband Atten. : 60.0697 dB Transition Width : 0.05 ```
```mq = measure(Hq) ```
```mq = Sample Rate : N/A (normalized frequency) Passband Edge : 0.4 3-dB Point : 0.41178 6-dB Point : 0.41845 Stopband Edge : 0.45 Passband Ripple : 0.49773 dB Stopband Atten. : 59.9728 dB Transition Width : 0.05 ```
```hfvt=fvtool(Hd,Hq,'ShowReference','off'); legend(hfvt,'Floating-point Filter','Fixed-point Filter'); ```