of Microprocessors

MUSIC SYNTHESIS SOFTWARE 699
Many other possibilities should come to mind. In fact, the appearance
of the input language need not even bear a resemblance to NOTRAN. In this
respeer, "basic NOTRAN" would be used as a musical "machine language"
with a high-level compiler generating code for it.
Level 0 Routines
Although seemingly out of sequence, Level 0 routines are discussed
here because for most microcomputer direct synthesis installations they
would comprise a separate program and separate pass of the data. As mentioned
earlier, Level 0 routines operate on the individual sound samples
produced by the Levell routines to introduce reverberation, choral effeers,
etc. The reader should not underestimate the utility of these simple techniques
in enhancing and "de-mechanizing" the sound of even the most
sophisticated synthesis methods.
The techniques described in Chapter 14, however, require large
amounts of memory for simulated delay lines and therefore would probably
not fit if implemented as part of the synthesis program. Thus, Level 0
functions would be written to read a sample stream from a mass storage
device, process it, and write the altered stream on another device.
In some cases, the "acoustical environment" created by the Level 0
routines must change during the course of the score. If the ability to dynamically
specify reverberation parameters is desired, the Level 0 program will
also have to scan the score while processing the sample string. Virtually all of
the score data will be ignored, but timing will have to be followed to
determine where in the sample string to change reverberation parameters.
Sample Storage Devices
The mass-storage device used to hold computed sample data usually
determines a delayed playback synthesis system's performance in two ways.
First, its average data transfer rate limits the number of channels, sample size,
and ultimately the sample rate that can be used. "Average" was emphasized
because this figure is often much lower than the peak transfer rate often
quoted in sales literature. With a disk, for example, nonproductive gaps
between sectors, finite head movement time from one track to the next, and
sector format restrictions, all subtract from theoretical average transfer rates.
If the sample data are read using the computer's operating system as opposed
to direct programming of the hardware, severe performance degradation can
often occur due to operating system overhead. A lO-to-l slowdown is not
uncommon, thus making direct hardware programming a necessity in many
cases.
The other performance determinant is, ofcourse, mass-storage capacity.
How storage capacity relates to continuous time capacity and other variables
can be determined by applying these very simple formulas: