In this section, we’ll look at how MIDI is handled in practice.
First, let’s consider a very simple scenario where you’re generating electronic music in a live performance. In this situation, you need only a MIDI controller and a synthesizer. The controller collects the performance information from the musician and transmits that data to the synthesizer. The synthesizer in turn generates a sound based on the incoming control data. This all happens in real-time, the assumption being that there is no need to record the performance.
Now suppose you want also want to capture the musician’s performance. In this situation, you have two options. The first option involves setting up a microphone and making an audio recording of the sounds produced by the synthesizer during the performance. This option is fine assuming you don’t ever need to change the performance, and you have the resources to deal with the large file size of the digital audio recording.
The second option is simply to capture the MIDI performance data coming from the controller. The advantage here is that the MIDI control messages constitute much less data than the data that would be generated if a synthesizer were to transform the performance into digital audio. Another advantage to storing in MIDI format is that you can go back later and easily change the MIDI messages, which generally is a much easier process than digital audio processing. If the musician played a wrong note, all you need to do is change the data byte representing that note number, and when the stored MIDI control data is played back into the synthesizer, the synthesizer generates the correct sound. In contrast, there’s no easy way to change individual notes in a digital audio recording. Pitch correction plug-ins can be applied to digital audio, but they potentially distort your sound, and sometimes can’t fix the error at all.
So let’s say you go with option two. For this, you need a MIDI sequencer between the controller and the synthesizer. The sequencer captures the MIDI data from the controller and sends it on to the synthesizer. This MIDI data is stored in the computer. Later, the sequencer can recall the stored MIDI data and send it again to the synthesizer, thereby perfectly recreating the original performance.
The next questions to consider are these: Which parts of this setup are hardware and which are software? And how do these components communicate with each other? Four different configurations for linking controllers, sequencers, and synthesizers are diagrammed in Figure 6.28. We’ll describe each of these in turn.
In the early days of MIDI, hardware synthesizers were the norm, and dedicated hardware sequencers also existed, like the one shown in Figure 6.29. Thus, an entire MIDI setup could be accomplished through hardware, as diagrammed in Option 1 of Figure 6.28.
Now that personal computers have ample memory and large external drives, software solutions are more common. A standard setup is to have a MIDI controller keyboard connected to your computer via USB or through a USB MIDI interface like the one shown in Figure 6.30. Software on the computer serves the role of sequencer and synthesizer. Sometimes one program can serve both roles, as diagrammed in Option 2 of Figure 6.28. This is the case, for example, with both Cakewalk Sonar and Apple Logic, which provide a sequencer and built-in soft synths. Sonar’s sample-based soft synth is called the TTS, shown in Figure 6.31. Because samplers and synthesizers are often made by third party companies and then incorporated into software sequencers, they can be referred to as plug-ins. Logic and Sonar have numerous plug-ins that are automatically installed – for example, the EXS24 sampler (Figure 6.32) and the EFM1 FM synthesizer (Figure 6.33).
[aside]As you work with MIDI and digital audio, you’ll develop a large vocabulary of abbreviations and acronyms. In the area of plug-ins, the abbreviations relate to standardized formats that allow various software components to communicate with each other. VSTi stands for virtual studio technology instrument, created and licensed by Steinberg. This is one of the most widely used formats. Dxi is a plug-in format based on Microsoft Direct X, and is a Windows-based format. AU, standing for audio unit, is a Mac-based format. MAS refers to plug-ins that work with Digital Performer, an audio/MIDI processing system created by the MOTU company. RTAS (Real-Time AudioSuite) is the protocol developed by Digidesin for Pro Tools. You need to know which formats are compatible on which platforms. You can find the most recent information through the documentation of your software or through on-line sources.[/aside]
Some third-party vendor samplers and synthesizers are not automatically installed with a software sequencer, but they can be added by means of a software wrapper. The software wrapper makes it possible for the plug-in to run natively inside the sequencer software. This way you can use the sequencer’s native audio and MIDI engine and avoid the problem of having several programs running at once and having to save your work in multiple formats. Typically what happens is a developer creates a standalone soft synth like the one shown in Figure 6.34. He can then create an Audio Unit wrapper that allows his program to be inserted as an Audio Unit instrument, as shown for Logic in Figure 6.35. He can also create a VSTi wrapper for his synthesizer that allows the program to be inserted as a VSTi instrument in a program like Cakewalk, an MAS wrapper for MOTU Digital Performer, and so forth. A setup like this is shown in Option 3 of Figure 6.28.
An alternative to built-in synths or installed plug-ins is to have more than one program running on your computer, each serving a different function to create the music. An example of such a configuration would be to use Sonar or Logic as your sequencer, and then use Reason to provide a wide array of samplers and synthesizers. This setup introduces a new question: How do the different software programs communicate with each other?
One strategy is to create little software objects that pretend to be MIDI or audio inputs and outputs on the computer. Instead of linking directly to input and output hardware on the computer, you use these software objects as virtual cables. That is, the output from the MIDI sequencer program goes to the input of the software object, and the output of the software object goes to the input of the MIDI synthesis program. The software object functions as a virtual wire between the sequencer and synthesizer. The audio signal output by the soft synth can be routed directly to a physical audio output on your hardware audio interface, to a separate audio recording program, or back into the sequencer program to be stored as sampled audio data. This configuration is diagrammed in Option 4 of Figure 6.28.
An example of this virtual wire strategy is the Rewire technology developed by Propellerhead and used with its sampler/synthesizer program, Reason. Figure 6.36 shows how a track in Sonar can be rewired to connect to a sampler in Reason. The track labeled “MIDI to Reason” has the MIDI controller as its input and Reason as its output. The NN-XT sampler in Reason translates the MIDI commands into digital audio and sends the audio back to the track labeled “Reason to audio.” This track sends the audio output to the sound card.
Other virtual wiring technologies are available. Soundflower is another program for Mac OS X developed by Cycling ’74 that creates virtual audio wires that can be routed between programs. CoreMIDI Virtual Ports are integrated into Apple’s CoreMIDI framework on Mac OS X. A similar technology called MIDI Yoke (developed by a third party) works in the Windows operating systems. Jack is an open source tool that runs on Windows, Mac OS X, and various UNIX platforms to create virtual MIDI and audio objects.