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3]SOUND SAMPLING 
3]By Scott L. Wilcox 
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     Sampling is like digital tape recording. The sampler converts the analog
audio signal into digital information. As such it can be stored on disk or
integrated into a program. Compact disks use digital sampling to record. An
analog-to-digital converter (A/D) is used to record the music or sound in
digital format. The digital information is written to the CD, where it can be
played from the CD player, which is simply a computer with a digital-to-
analog (D/A) converter. There is no loss of sound quality with CDs as there
is in analog recording --tapes and records.
     Consider an analog recording like an oil painting. It looks beautiful,
but as time passes, the colors fade and some of the paint chips off. The
digital recording is like a book about the painting, that you are able to
plug into a box and mysteriously produce the exact painting. As long as you
can read the writing in the book, even if it gets a little dog-eared, the
image can be exactly reproduced. So it is with digital sampling. As long as
the information can be read from the storage media, the original sound will
be reproduced. 

3]BITS, RATES AND RESOLUTION
     Just as digital graphics have different resolution --320x200, 640x400,
etc. --so does digital sound. And as graphics resolution is measured in how
many pixels are available on screen, digital sound resolution is measured in
samples per second, or how many "slices" of sound are taken in a second of
recording. A sampling rate of 10,000 samples per second will have a lower
resolution than one of 20,000.
     "Bits" in sample resolution refers to the "word" size used to describe
each sample or slice of sound. 16-bit is CD quality and is said to be the
highest resolution the human ear can detect. An 8-bit word is half the size
of 16-bit and cannot capture some of the finer details of a sound.
     You might think that the Amiga, since it has a 16/32 bit CPU with the
68000, would be a 16-bit sampler. It isn't.  The sound handling co-processor
is 8-bit, and it handles all the digital-to-analog converting. Don't despair,
8-bit samplers still sound very good.  In fact, probably the best selling
musical sampler in the world is the 8-bit Mirage made by Ensoniq. Plus, the
Amiga can process those 8-bit samples with its 16/32 bit CPU, which can
improve the sample.

3]SAMPLING HARDWARE
     You've got the Amiga and you're ready to capture some amazing sounds for
your programs and musical compositions. To play the sounds, you only need the
Amiga, with its built in D/A converter. But to record the samples, you need
hardware with an A/D converter and some way of feeding it to the Amiga.
     There are many commercial samplers that plug into various ports on the
Amiga, and there are plans for one in the February 1989 issue of Amazing
Computing if you want to build your own.
     Next, you need some kind of software to use with your sampler. The
commercial samplers come with their own sampling software, and there are many
software packages that work with different samplers.
     Your hardware is plugged in. Your software is running. All you need is a
sound source. If you are sampling "live," you also need a microphone, quiet,
and good acoustics. An inexpensive condenser microphone, the kind with the
battery, makes a very good sampling mike. A room without many hard, flat
surfaces will probably suffice for your recording studio. Quiet is very
important for successful sampling.

3]SAMPLE DOWN, DUDE
     Set the sampling rate with the software to achieve the desired effect.
If you want small samples and quality is not so important, choose a lower
rate.  If the sound is complex and detailed and you need a higher resolution,
choose a higher rate. You will have to juggle sound resolution, length of
sample, and storage size to find the balance for your purposes. Speech,
simpler sounds like drums and some sound effects can be sampled at a lower
rate and still be adequate. The software package will have some way to
monitor the incoming signal so you can set the recording levels. If you are
sampling with a microphone, this should be done with headphones to eliminate
feedback. You want a strong signal without aliasing (distortion) or clipping.
Turn up the volume on other sound sources --tape player, CD player, VCR,
stereo --until the signal distorts, then back it off until it is clear and
clean. If your hardware has any adjustments, make them to suit you. It is
your sample, your ears must be the judge.
     An equalizer is a very useful tool when making samples, especially if it
has seven bands or more. You can adjust the levels of the EQ to get the
effect that you want. Experiment with it. Boost the high frequencies for some
added sparkle in your sample. Now set the length in seconds of the sample, if
your software allows that. Set it longer than you need. You can edit it later
and take the sample. Look at a graphical display of your sample. Are any of
the tops or bottoms of the soundwave clipped, or flattened? If so, then turn
the volume down and sample again.  Don't get too close if you are using a
mike.
     Does the sample look small? It should fill the screen of the graphic
display. You want it to be as full as possible without any clipping. Turn the
volume up, and/or adjust the software recording level until it is just right.
     Once you are satisfied with the sample, you are ready to edit it. Most
sampler software has some kind of graphical editor. Pull a slider (or
whatever) to set the beginning and end of the sample to where you want them.
If you will be looping the sample (playing it continuously), set the loop
point, too. Now save the edited sample. It's there waiting to be used.
     For under $100 you can add digital sound sampling to your Amiga. It
makes a useful and fun addition to your computer. With a little practice, you
can make high quality samples for business or pleasure.

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