MIDI Monitor Written in Visual Basic

• Download source code - 127.7 KB

Introduction

This article presents a MIDI monitor written in VB, using Visual Basic Express 2010.

Being curious what MIDI data is exactly outputted by my MIDI keyboard, I decided to write this little tool.

Using the Code

After reading several articles on CodeProject, it turned out that callbacks and delegates were needed to capture and display the MIDI data. Being unfamiliar with them, it was time to start coding and find out myself.

First the complete code:

Imports System.Threading
Imports System.Runtime.InteropServices

Public Class Form1

    Public Declare Function midiInGetNumDevs Lib "winmm.dll" () As Integer
    Public Declare Function midiInGetDevCaps Lib "winmm.dll" _
           Alias "midiInGetDevCapsA" (ByVal uDeviceID As Integer, _
           ByRef lpCaps As MIDIINCAPS, ByVal uSize As Integer) As Integer
    Public Declare Function midiInOpen Lib "winmm.dll" _
           (ByRef hMidiIn As Integer, ByVal uDeviceID As Integer, _
           ByVal dwCallback As MidiInCallback, ByVal dwInstance As Integer, _
           ByVal dwFlags As Integer) As Integer
    Public Declare Function midiInStart Lib "winmm.dll" (ByVal hMidiIn As Integer) As Integer
    Public Declare Function midiInStop Lib "winmm.dll" (ByVal hMidiIn As Integer) As Integer
    Public Declare Function midiInReset Lib "winmm.dll" (ByVal hMidiIn As Integer) As Integer
    Public Declare Function midiInClose Lib "winmm.dll" (ByVal hMidiIn As Integer) As Integer

    Public Delegate Function MidiInCallback(ByVal hMidiIn As Integer, _
           ByVal wMsg As UInteger, ByVal dwInstance As Integer, _
           ByVal dwParam1 As Integer, ByVal dwParam2 As Integer) As Integer
    Public ptrCallback As New MidiInCallback(AddressOf MidiInProc)
    Public Const CALLBACK_FUNCTION As Integer = &H30000
    Public Const MIDI_IO_STATUS = &H20

    Public Delegate Sub DisplayDataDelegate(dwParam1)

    Public Structure MIDIINCAPS
        Dim wMid As Int16 ' Manufacturer ID
        Dim wPid As Int16 ' Product ID
        Dim vDriverVersion As Integer ' Driver version
        <MarshalAs(UnmanagedType.ByValTStr, SizeConst:=32)> _
        Dim szPname As String ' Product Name
        Dim dwSupport As Integer ' Reserved
    End Structure

    Dim hMidiIn As Integer
    Dim StatusByte As Byte
    Dim DataByte1 As Byte
    Dim DataByte2 As Byte
    Dim MonitorActive As Boolean = False
    Dim HideMidiSysMessages As Boolean = False

    Function MidiInProc(ByVal hMidiIn As Integer, _
        ByVal wMsg As UInteger, ByVal dwInstance As Integer, _
        ByVal dwParam1 As Integer, ByVal dwParam2 As Integer) As Integer
        If MonitorActive = True Then
            TextBox1.Invoke(New DisplayDataDelegate(AddressOf DisplayData), _
                            New Object() {dwParam1})
        End If
    End Function

    Private Sub DisplayData(dwParam1)
        If ((HideMidiSysMessages = True) And ((dwParam1 And &HF0) = &HF0)) Then
            Exit Sub
        Else
            StatusByte = (dwParam1 And &HFF)
            DataByte1 = (dwParam1 And &HFF00) >> 8
            DataByte2 = (dwParam1 And &HFF0000) >> 16
            TextBox1.AppendText(String.Format("{0:X2} {1:X2} {2:X2}{3}", _
                                StatusByte, DataByte1, DataByte2, vbCrLf))
        End If
    End Sub

    Private Sub Form1_Load(ByVal sender As Object, _
            ByVal e As System.EventArgs) Handles Me.Load
        Me.Show()
        If midiInGetNumDevs() = 0 Then
            MsgBox("No MIDI devices connected")
            Application.Exit()
        End If

        Dim InCaps As New MIDIINCAPS
        Dim DevCnt As Integer

        For DevCnt = 0 To (midiInGetNumDevs - 1)
            midiInGetDevCaps(DevCnt, InCaps, Len(InCaps))
            ComboBox1.Items.Add(InCaps.szPname)
        Next DevCnt
    End Sub

    Private Sub ComboBox1_SelectedIndexChanged(sender As System.Object, _
            e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
        ComboBox1.Enabled = False
        Dim DeviceID As Integer = ComboBox1.SelectedIndex
        midiInOpen(hMidiIn, DeviceID, ptrCallback, 0, CALLBACK_FUNCTION Or MIDI_IO_STATUS)
        midiInStart(hMidiIn)
        MonitorActive = True
        Button2.Text = "Stop monitor"
    End Sub

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) _
            Handles Button1.Click
        TextBox1.Clear()
    End Sub

    Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) _
            Handles Button2.Click
        If MonitorActive = False Then
            midiInStart(hMidiIn)
            MonitorActive = True
            Button2.Text = "Stop monitor"
        Else
            midiInStop(hMidiIn)
            MonitorActive = False
            Button2.Text = "Start monitor"
        End If
    End Sub

    Private Sub Button3_Click(sender As System.Object, e As System.EventArgs) _
            Handles Button3.Click
        If HideMidiSysMessages = False Then
            HideMidiSysMessages = True
            Button3.Text = "Show System messages"
        Else
            HideMidiSysMessages = False
            Button3.Text = "Hide System messages"
        End If
    End Sub

    Private Sub Form1_FormClosed(ByVal sender As Object, _
            ByVal e As System.Windows.Forms.FormClosedEventArgs) Handles Me.FormClosed
        MonitorActive = False
        midiInStop(hMidiIn)
        midiInReset(hMidiIn)
        'midiInClose(hMidiIn)
        Application.Exit()
    End Sub

End Class

Details

The source code is rather self-explanatory. You might want to check out the MIDI reference on the MSDN website for in-depth information for details on the different functions.

Below, I highlighted the parts that took me a while to figure out:

Function MidiInProc(ByVal hMidiIn As Integer, ByVal wMsg As UInteger, _
         ByVal dwInstance As Integer, ByVal dwParam1 As Integer, _
         ByVal dwParam2 As Integer) As Integer
    If MonitorActive = True Then
        TextBox1.Invoke(New DisplayDataDelegate(AddressOf DisplayData), _
                        New Object() {dwParam1})
    End If
End Function

This is the callback function which returns the incoming MIDI messages. dwParam1 contains the 4 bytes MIDI data that I am looking for. From MSDN:

dwMidiMessage

MIDI message that was received. The message is packed into a doubleword value as follows:

High word	High-order byte	Not used
	Low-order byte	Contains a second byte of MIDI data (when needed)
Low word	High-order byte	Contains the first byte of MIDI data (when needed)
	Low-order byte	Contains the MIDI status

From within the callback function, "DisplayDataDelegate" is invoked to display the received MIDI data.

Private Sub DisplayData(dwParam1)
    If ((HideMidiSysMessages = True) And ((dwParam1 And &HF0) = &HF0)) Then
        Exit Sub
    Else
        StatusByte = (dwParam1 And &HFF)
        DataByte1 = (dwParam1 And &HFF00) >> 8
        DataByte2 = (dwParam1 And &HFF0000) >> 16
        TextBox1.AppendText(String.Format("{0:X2} {1:X2} {2:X2}{3}", _
                            StatusByte, DataByte1, DataByte2, vbCrLf))
    End If
End Sub

This sub formats the dwParam1 bytes and displays them in the textbox.

The HideMidiSysMessages toggle has been added to suppress the continuous "FE" messages (Active Sensing) my MIDI keyboard is generating.

As a side note: I also found that my MIDI keyboard does not generate a Note Off message but a Note On with velocity '00' when releasing a key (see the screendump above).

Public ptrCallback As New MidiInCallback(AddressOf MidiInProc)

This line makes a permanent reference to the callback function. If you don't do this, the callback function will be GarbageCollected by .NET.

'midiInClose(hMidiIn)

This line is commented out because sometimes midiInClose(hMidiIn) hangs (meaning: it does not return with or without an error, just hangs). The error shown by the debugger is "Argument not specified for parameter 'hMidiIn' of 'Public Shared Function midiInClose(hMidiIn As Integer) As Integer" (?)

The hanging situation only occurs when a lot of MIDI data is generated by the MIDI keyboard while trying to execute midiInClose. I found an interesting and indepth article here on this issue [kudos to "Les"].

My guess is that midiInClose hangs because MidiInProc is still processing incoming MIDI data. I have no idea how to solve or workaround this issue.

But Application.Exit() definitely ends the program without complaints or leaving threads/callback functions running in the background.

If anyone knows a solution for the midiInClose issue, please feel free to comment!

Final Words

Writing this little program was an interesting exercise in dealing with delegates and callback functions in VB. I'm sure a professional programmer [which I'm surely not] will see improvements, so shoot!

In the ZIP file, you will also find a ready-to-run EXE file (in \bin\Release). It runs on Win XP and Windows 7 32 & 64 bit.

History

• Rev A: First out
• Rev B: An MIDI device input selector was added and comments from people that replied below were incorporated