Nov 23 1988

        Tips and Tricks - impress your friends, mystify your enemies

RGS.doc has a few tricks mentioned it it, but I thought I'd give a few
more as a tutorial.

Educational Division:

One of the things which is a little hard to understand about RGS is the
phase or frequency axis. What exactly is this, and what are those numbers?
RGS works by summing sine waves together. Sinewaves repeat themselves
endlessly. The number of complete cycles which occur in a second is the
frequency of the sinewave, measured in Cyles/Second or Hertz (Hz). If you
use digital synthesis to make a sinewave, you must approximate the  true
shape of the wave with little stair-steps. When the frequency is high, the
number of sinewaves per second is also high. Since a sample is a fixed
length, the wavelength of the sinewave must correspondingly decrease.
Clearly, you cannot have a representation of a wave which  has a wavelength
less than 1 sample long. As a matter of fact, you should have at least two
samples per wave-cycle if you hope to have even the least  accurate sine
representation. So, the little number with the decimal point in D)oodle mode
is the number of samples needed to represent one wave-cycle. It usually
increases toward the bottom of the screen geometrically. The is because
lower sounds have longer wavelengths. How is it possible to have fractional
samples/cycle? Because I precisely line each sinewave up after the previous
on on its left, on the average the number of samples will be fractional. In
the long run, it will sound correctly. Remember that each spot on the screen
represents several samples (up to 256). The reason this number is multiplied
by 100 in the R)eset and B)PF mode dialogs is merely laziness.
There is no number corresponding to frequency: The frequency of the sound
will change when the Amiga  Period changes. The Amiga period is  a number
which governs the delay between the playing of successive samples, and
runs from 124 up. The time represented by one of these delay units (color
clocks) is 0.279365 microseconds. 


About IFF 8SVX files. 

The IFF 8SVX sound file format is documented in the Rom Kernal Guide:Exec
volume. Each sound has a name, some idea of its tuning, and a number
of octaves of different samples. The reason separate octaves are used
is that the normal way of playing samples on an Amiga involves playing
with the Amiga preiod number. While it is best for fidelity to have a long
sample played at a high speed, high notes bump into that 124 color clock 
limit. So, at some sacrifice in fidelity , a sample half as long is used,
with the sound of the lower octave sped up. RGS places the sample you
hear in play mode as the lowest octave (most accurate). The higher octaves
are derived from this high-quality sample by choosing every other sample
in the lower octave. This is, strictly speaking, inaccurate (the average
should really be done, at least. True frequency changing involves much
more complex mathematics). However, it's usually OK.


Neat Stuff Department:

Set the harmonic space to 400,0 (4 sample on the top line).
Draw a spectrogram in buffer A and synthesize it. Flip to Buffer B
with the A key. Draw the 'top octave' of the spectrum in the usual way,
resetting the space to 200,400. Flip back to the A buffer. Zone the
entire screen. Turn on the Real time synthesis. Do Copy Zone A/B. It will
mix the new synthesis into the existing sound, adding the top octave to
the sound! Future versions of RGS may have similar mixing and harmonic
appendage tricks built in. This works best if you work with the volume
set to '1' (highest). Make sure not to overload!

Rhythm effects can be done by making skinny Blobs and laying them down
while the time is grid-locked (the keypad 4 and 6 keys). Use the
Filt mode to ramp up to a beat, or use ramp up or down. Throw some
Ramps on top of this mess - if you lock the frequencies you can make a quick
Buzz on the beat.

Develop a spectrogram, but leave a frequency band clear across the whole
sample. Zone this empty band. Find a nice Amiga period (Play mode) and lock
it with  the ~ key.  Set sample mode 3 (real 3 key). X)ynth the zone, 
clearing the sound, but stay in Real-time synth mode. Now , stick your
fingers on the x and y keys. Use Z to zone a block of spectrum. Use X
to synthesize it. Repeat endlessly. I restart the playback after Xynthing,
but otherwise, you can mix in bands of various hoo-hah in realtime.

Time lock to 2 or 3 (hit keypad 6 once or twice). Using a tiny Blob
or Dot, sprinkle dotty lines on the screen. Nice, ratchety sound, eh?
Sounds vocal almost. Blur the dots with Filt. If you like, gridlock
the frequencies as well. Or use Formant.

Using a big blob, with the synthesis off, Make a colorful mess on the
screen. Use FilC and Filt to smooth the colors out. Select Xclude and
carve a harmonic staff through the mess. Filter to taste. Go to UltraMidi
and wake the neighbors.

Bandpassfilter a sample with a voice and accompaniment. Make it Accurate
(K=10). Save the  spectrogram - it took forever to do didn't it? Now
copy it to the other buffer as insurance. Look at the harmonic lines
in the voice's spectrum - they should be distinguished from the
accompaniment. Find the highest continuous harmonic in the voice you can.
(If not strictly continuous, it's OK) . Reset the Harmonic handle to 
this harmonic's number (Up and Down Arrows). Use xclud to carve the 
voice out of the background by following the selected harmonic with the
pointer. You can fix mistakes by zoning and using Copy zone A/B (see
why you saved it to the other buffer?) Now synthesize. Voice should be 
isolated.