02_13_1B
additional parameters: irise, idec


This design uses a LINSEG envelope which is different from the
previous one. The envelope produces a large and fast increase of
the amplitudes in the rise. Both for instruments 02_13_1 and
02_13_1B the rise time itself is 50 msec. It is somewhat larger
than in most actual trumpet sounds because of the unusual way in
which the harmonics enter.

Risset adds here that these sounds are not presented as good
imitations of trumpet sounds. There is no formant structure,
there are not enough components and there is no frequency
control. Yet, he points out, this design is not limited to
brass-like sounds, and can be useful in other contexts. 

The figure shows that below an amplitude of 33 the output will
contain no harmonics, while for values between 33 and 50 the
number of harmonic components increases to seven.

Reaching 50 on the abscissa, all functions are .05. This can be
used as a point of reference, to understand how the quantities
are distributed in this instrument. After passing through the
sloped linear scaling functions, the amplitudes are multiplied by
different amounts, proportional to 1000. For the second harmonic:
1000x.05=50, for the third harmonic: 2000x.05=100 and so on for
the other harmonics. These amounts function as additional (or
secondary) weighting factors of the harmonics.

While all following the LINSEG envelope, above an amplitude value
of 50, the various harmonics increase 2,3 ... 7 times as fast as
the fundamental (according to their harmonic number in this
particular design). (Risset 1969: #210)

(illustration harmonic scheme)

For implementations of this type of design, a multiplier before
the output is used to scale the amplitude to the desired level.
Any attempt to scale at an earlier stage would disturb the
precarious balance of this instrument, as will be clear from the
detailed exposition above.


(.orc and .sco files)

