How is music technology being used today to inspire creative applications in music? In this paper, I focus in on software programs that record and edit both MIDI and digital audio. These software programs are known as digital audio sequencers.
    The total integration of MIDI and digital audio has been a significant technological development for musicians in recent years. The ever-increasing power of desktop computers, combined with the advent of inexpensive, dedicated sound hardware that can be added to a computer, has resulted in a dual pairing of these two worlds of sound manipulation. As software appears that brings MIDI and digital audio together, an enormous realm of creative possibilities has opened up. By taking advantage of both the efficiency of MIDI and the flexibility of digital audio, digital audio sequencers open up new dimensions of creative expression in the classroom and for the computer composer.

Benefits of Using Midi and Digital Audio Together
    There are numerous practical advantages to controlling both MIDI sequencing and digital audio recording simultaneously. MIDI composers are used to cutting and pasting musical events as easily as paragraphs in a word processor, and the tools for doing so have become highly sophisticated and friendly. Extending that metaphor to blocks of digital audio is a major advantage. For example, digital audio can also be processed and mixed non-destructively in the same way that MIDI tracks can be faded, panned, or processed using various controller commands within the sequenced data.
    Additionally, since much MIDI-based music often seems to have a tendency to sound mechanical, the addition of using digital audio can often add greater realism, naturalness, and feeling to the sounds controlled by MIDI.
Digital audio sequencers can play both audio and MIDI tracks simultaneously. In fact, all major MIDI sequencing software programs now include the ability to record, edit, and integrate digital audio directly with MIDI. Since audio and MIDI tracks are displayed together on screen, it is now much easier to conceptualize both NMI and digital audio together. This simultaneous visualization of both MIDI and digital audio gives the composer or sound designer instant visual feedback on the structure of a piece, either as an overview, or at the microscopic editing level. Instead of being separate entities that happen to be synchronized, the audio and MIDI data can be seen as a single compositional entity, giving the musician a vastly improved platform for creativity.

How Does It Work?
    From a hardware standpoint, the key to integrating MIDI and digital audio has been the development of sound-recording and sound-generating hardware placed inside the computer that is handling the MIDI data. MIDI's bandwidth over sixteen channels of data is limited to 31,250 bits per second, which is extremely trivial for a computer whose CPU is ticking at several million clock cycles per second. Audio, however, is much more demanding, and bandwidths in excess of 1.5 million bits per second are possible with just two tracks. Audio, therefore, is often produced by a plug-in card that can handle all the sound-generating calculations itself and be addressed directly by the computer, bypassing the need to use the computer's central processing unit (CPU). The major differences between the various products available, besides the platforms they are designed for, have to do with the method and speed of data transfer and the audio quality. These differences are in terms of sampling rate (which controls frequency response) and number of bits resolution (which determines dynamic range).
    In digital audio sequencers, both MIDI and audio data are often pictured as "clips" of information. A "clip" view is especially suited to edit operations involving both MIDI and audio for cutting, copying, and pasting. Illustrated below is a "clip" view of two MIDI tracks on the right-hand side (with a "track" view on the left). The numbers above the clips refer to measures of music. The actual contents of these clips contain MIDI performance information. The black-mark drawings within each clip are drawn in such a way as to suggest the density of the various notes that occur within each track. These tracks were recorded into the computer via a NMI synthesizer.

    The next example shows how the above MIDI clips might be edited. The Bass Line (Track 2) clip has been tripled in length by copying the Bass Line clip and pasting two more copies of it end to end. Then the Bass Line track has been "combined" into one long track. The Chords track (Track 1) has been edited the same way as Track 2 but has not been "combined," and so exists as three separate clips.

    The next illustration shows the recording of a digital audio track (Track 5). The clip in track 5 represents the recording of actual sound as opposed to tracks one through three which represent MIDI performance information.

    Audio or recorded sound is edited independently of the MIDI data. Here is a close-up view of some waveform data recorded on track 5. It uses the same "clip" format as did the MIDI tracks.

    Here is the same data after it has been edited. Here, the track has been normalized, that is, the volume has been raised to the greatest possible level without distortion.

    Other ways to edit digital audio include equalization, fading in or out, reversing, using reverb, chorusing, flanging, time compression or expansion, and mixing audio tracks together.
    An especially convenient way to view MIDI data is, of course, the staff view, as illustrated next.
    Here are tracks 1 and 2 being viewed through the "staff view" option:

    For some tasks, standard musical notation provides the most natural and intuitive form for viewing and editing music. Staff view lets you manipulate notes as combinations of pitch and duration. It suppresses the display of other MIDI information such as MIDI channel and velocity. Selecting, copying, and transposing notes, for example, are simple operations in Staff view.
    Besides track, clip, and audio view, digital audio sequencers also have an event view where individual MIDI and audio events may be looked at and edited sequentially in the form of a "list." Additionally, a "faders" view may be present which permits you to record fader moves in real-time effecting both N41DI and digital audio volume and panning.

Conclusion
    The technology explosion of the last two decades has brought down many barriers, including that between MIDI and digital audio. By adding digital audio to MIDI, it can often make MIDI-based music sound much more realistic and less mechanical. Hence, many different hardware and software companies are gearing their developments toward integrating these two ways of producing music in ways previously undreamed of The supreme representative of this union is the digital audio sequencer. By taking advantage of both the efficiency of MIDI and the flexibility of digital audio, digital audio sequencers open up new dimensions of creative expression for the computer composer. It has become the ideal tool in technology today to inspire musical creativity.