How can I change the SNR over trials in a staircase threshold?

Hello everyone!

I have a task which consists in presenting for 20 times a beep signal of 5 different pitches immerse in noise. In the end I would have 100 presentations, 20 for each pitch of the signal. The signal must be presented randomly to one ear at a time and, depending on the response of the subject, the SNR must increase or decrease. Here is my code (sorry it's quite long!):

samplingRate = 48000;
myPitches = [500, 1000, 1500, 2000, 2500]; 
howLong = .5;
[beep] = MakeBeep(500, howLong, samplingRate); % I only need this to make the noise
noise = rand(size(beep));
mySNR = .1; % initial value
condition_fs = [1 2 3 4 5]; 
numCondition = {'1', '2'}; % left and right
% Start presentation
RandPitches = Shuffle(myPitches); %Randomising order of pitches
presentedPitches = [];
subSNR = [];
for condition_fs = 1:5 % five frequencies
    for trial = 1:20 % presentation for each frequency
        pause(1.5)
        [beep] = MakeBeep(RandPitches(condition_fs), howLong, samplingRate); % each pitch is presented for 20 times
        presentedPitches(condition_fs, trial) = RandPitches(condition_fs); % save pitches
        
        % Randomising ear presentation
        RandCondition = randperm(length(numCondition),1);
        if RandCondition == 1 % if the randperm gives 1, then play left_ear
            left_ear = [beep+noise; noise].*mySNR;
            PsychPortAudio('FillBuffer', pahandle, left_ear)
            PsychPortAudio('Start', pahandle)
        else
            % if condition 2 (beep right) then play stimulus with beep right
            right_ear = [noise; beep+noise].*mySNR;
            PsychPortAudio('FillBuffer', pahandle, right_ear);
            PsychPortAudio('Start', pahandle);
        end
    end
    
    % interpreting key press
    keyPress = false;
    while ~keyPress
        [keyPress, pressTime, keyCode] = KbCheck(-1);
    end
    keyName = KbName(keyCode);
    
      if keyName(1) == 'q'
          disp('exiting')
          sca
          break
      end
      % This if statement should terminate the experiment if q is pressed
      
      if keyName(1) == '1' && RandCondition == 1 % Correct answer, response matches presentation
          mySNR = mySNR*.9; % decrease by 10%
      else % if response does not match presentation
          mySNR = mySNR*1.1; % increase by 10%
      end
      
      if keyName(1) == '9' && RandCondition == 2 % Correct answer, response matches presentation
          mySNR = mySNR*.9;
      else
          mySNR = mySNR*1.1;
      end
    % Save each mySNR in a variable
    subSNR(condition_fs, trial) = mySNR; % 5 rows_fs and 20 columns_trials    
end

My main problem here is that the SNR does not change over trials. In the subSNR are stored all zeros, except in the very last trial.

I guess my problem regards the interpretation of the keypress. I tried everything to solve it, but I fail all the time! I really hope someone is able to help me here!

Thank you!