envelope detection false amplitude problem

Hi all; ı used matlab envelope detection simulink modal(squaring signal and low pass filtering ) and adapted for my wav data. It works but amplitude sometimes can't follow well. So can anyone suggest me about why it is happening?

function [sigenv1,sigenv1y] = zarfsimu(data,fs) %% Envelope Detection

le_data = length(data);

if le_data<1500 DownsampleFactor=3; end if le_data>=1500&&le_data<=2000 DownsampleFactor=round(le_data/375); end if le_data>2000&&le_data<=2500 DownsampleFactor=round(le_data/400); end if le_data>2500&&le_data<=3000 DownsampleFactor=round(le_data/400);end if le_data>3000&&le_data<=3500 DownsampleFactor=round(le_data/400);end if le_data>3500&&le_data<=4000 DownsampleFactor=round(le_data/400);end if le_data>4500 DownsampleFactor=round(le_data/1125);end

numSamples = 10000;% max sample frameSize = 10*DownsampleFactor; Fs=fs; hsin=dsp.SignalReader(data); %systemobject for data

for i=1:numSamples/frameSize

    sig=data;
    sigsq = 4*sig.*sig; %normally squaring data but i prefer four
    %a=downsample(sigsq, DownsampleFactor);    %downsampling
    %hm = mfilt.firdecim(15);
    hm = mfilt.firsrc(1,DownsampleFactor,[1 1]);
    des=filter(hm,sigsq);
    %low pass
    a1= firpm(30, [0 0.003 0.1 1], [1 1 0 0]);
    len_des=length(des);
    len=mod(len_des,length(a1));
    %if len ~= 0
           %add=length(a1)-len;
    add=15; % for plotting 
    all=len_des+add;
    des2=zeros(all,1);
    des2(1:len_des,1)=des; 

    a2=filter(a1,1,des2);
    %a=step(hlowpass1,des);
    sigenv1 = sqrt(a2);
    sigenv1y=sigenv1(15:end,1); 
end