You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: MidiDemo.m
    path of file: ./repos/HRTF-Individualization/model/matlabcode/functions/library/RealTimeAudioProcessor
    
    the code of the file until where you have to start completion: % MidiDemo
% 
% This is a real-time instrument derived from RealTimeAudioProdessor that
% uses MIDI input to generate audio. This works best when a low-latency
% driver like an ASIO driver is used for output (under Preferences::DSP
% Toolbox).
%
% Tucker McClure @ The MathWorks
% Copyright 2012 The MathWorks, Inc.

classdef MidiDemo < RealTimeAudioProcessor
    
    properties

        % Playback stuff
        keys = false(1, 128); % Logical array of keys currently down
        magnitudes = zeros(1, 128); % Magnitudes of down keys
        
    end

    properties (Constant = true)
        
        % Maps semitone steps about base frequency to correct frequency.
        % MIDI 
    
function out = stepImpl(rtap, time, ~)

            % Check for MIDI input.
            msgs = midi_interface();
            for k = 1:size(msgs, 2)
                
                msg = msgs(1, k);
                
                % Key down (with velocity > 0)
                if msg == 144 && msgs(3, k) > 0
                    
                    key = msgs(2, k)+1;
                    rtap.keys(key) = true;
                    rtap.magnitudes(key) = msgs(3, k)/127;
                    
                % Key up
                elseif msg == 128 || (msg == 144 && msgs(3, k) <= 0)
                    
                    rtap.keys(msgs(2, k)+1) = false;
                    
                % Aftertouch (polyphonic)
                elseif msg == 160
                    msgs(3, k)
                    rtap.magnitude(key) = msgs(3, k)/127;
                    
                end