impulse response (2012) feedback control system environment for two tenor
saxophones. Impulse response is a two-part sonic landscape. The first part
makes ...
i m p u l se r es po ns e 2012
for t wo t e n or sa x oph ones with ou t ai r an d c omput e r proc essi ng N o l an L e m
impulse response (2012)
feedback control system environment for two tenor saxophones
Impulse response is a two-part sonic landscape. The first part makes use of a feedback control system for the resonant conical chamber of the tenor saxophones. Two performers are directed to participate in a directed interplay of this feedback system. The following figure summarizes the orientation for this section:
feedback speaker 3
feedback speaker 1
performer 1
midi foot controller e.g. FCB1010
performer 2
computer Audio-interface*
computer Audio-interface*
midi foot controller e.g. FCB1010
(audience) speaker 2
speaker 4
* see more deailed block diagram
Referring to the previous diagram, the performers have control of 1. Filter presets (assigned to MIDI control presets via a MIDI foot controller) 2. Peak filter frequency (via left control expression pedal) 3. Gain (via right control expression pedal) In general, a multitude of feedback resonant frequencies can be induced from creating an “impulse” using the keys’ action mechanisms, fingering different notes and using the gain and or variable frequency pedals to shape the feedback. The performers have control of the different filter presets which enable an expanded pallete of feedback induced harmonics. In general, the most efficient technique to induce an impulse in the conical chamber is to use aggressively “finger” the low Bb and C keys and then quickly finger a different note while applying an increasing gain (via the right pedal). Alternatively, fingering a low Bb and then aggressively opening and closing only the D key can create a proper impulse. Experiment with cross fingerings during the envelopes of the feedback swells—they can create very interesting multi-phonics with complex timbres.
Furthermore, control over the resultant resonant frequency can be controlled using the variable frequency pedal on the midi foot controller. The preset filters are mostly “formant” style filters with several resonant peaks in their frequency response. The performer maintains control of one of the peaks and is able to “sweep” through the resonant peaks of the filter to induce different feedback resonances. The resonant peaks of the filter were designed to bring out certain resonances of the tenor saxophone. This mostly entailed manipulating the frequency responses of the low Bb (full tube length) and low C frequency response of the instrument.
Because this is a feedback system, the room in which it is to be performed can drastically change the frequency response of the system. Therefore, if possible, the piece should be “calibrated” in the room where it would be performed. This mostly applies the amount of distortion (see block diagram) and gain that should be applied for the scenario.
The first section is notated graphically. This can be interpreted in a number of ways. Most generally, the following axis describes the mapping of the axis in the graphic score:
general pitch
gain-volume envelope (for feedback swells)*
general impulse: key noise and fingering sounds
time * a gain-envelope implies that an impulse starts the feedback swell
This section can be performed in the following ways: - Each player follows the contours linearly (left to right, top to bottom) system by system. (the first player plays solo until indicated for the second player to join) - Each system is played one at a time—cues will determined when to move on to the next system. - Each systems is played out of order and chosen by the performers. - The graphic notation can be ignored and the players can improvise without notated elements within this format. Other symbols are not necessarily defined to be specific techniques. These are left undefined for the sake of the performers. As such, the notation used in this section was taken from waveforms that represented electrical activity from neurological processes in mice as measured from different parts of their brains.
*Other performance considerations: -The microphone should be placed inside the bell of the saxophone as much as possible to create an appropriate feedback loop. Because of this, a clippable instrument microphone is preferred (such as an AKG 419). -Addionally, the performer should experiment with the orientation of the feedback speaker with respect to their position. Depending on the live audio signal, the performance room and other factors, the microphone and the speaker should be at an distance so that the performer can accurately control the feedback swells (and so that unpleasant feedback can be avoided).
Section 2 Performance Notes The second section explores the industrial sounds of the saxophone’s mechanics As such, it uses samples taken from the action mechanisms on the saxophone. Much of the time, samples of key noise are over layed on top of one another, creating dense layers of mechanical noise. The samples of saxophone mechanism noise are notated with density contours.
These serve to show the performer’s visual cues so that the score can be more easily followed. Additionally, the use of bars indicating time durations help to facilitate the orientation of time with the pre-recording. Both saxophonists are asked to follow along a pre-recorded track that is triggered from the computer. The performers are to use only distortion in the live signal path without the use of the FIR filters in the first section (there should be no feedback path).
block diagram for DSP implementation ableton-max/msp files can be downloaded: www.nolanlem.com
feedback speaker
live audio e.g. AKG 419
footswitch 1: frequency control (50 - 470 Hz)
MIDI Foot Controller e.g. FCB1010
midi OUT
footswitch 2: foovariable gain (approx. -6dB-3dB) MIDI note presets (1-9)
variable gain
IIR FILTER*
reverb (0.5-2s)
“Phasor” Panning AM modulation
feedback path*
ADC
x
Computer block: via ableton-live/max-msp
DAC
speaker 2
* no feedback path for section 2
impulse response - I. feedback contours
53 sec.
[computer]
start track [ saxophone 1 ] [ saxophone 2 ]
4 &4 w Ÿ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
7.5 sec
5 1 & ™™ 4 + 8 œ >œ q=220
bœ
œ
œ
œ
™™
7 x
œ J
‘
6.25 s
5 1 & ™™ 4 + 8 œ >œ q=220
bœ
œ
œ
œ
™™
37 x x
œ J
‘ [4:3]
temporal ratio
16.5 x
q =165
? 45 + 81 b œ b>œ
œ
bœ
bœ
bœ J
œ
10 x
q=208
>œ 4 44 + 81 #œ œ œ œ œ œ œ & 4 #œ #œ œ œ œ #œ œ œ œ J
4 &4 #œ
3
œ
œ
œ
3
œ
œ
#œ
3
œ
œ
œ
3
œ
Œ
q=208
8 & 4 #œ
œ
œ
3x
4x
3x
4x
? 44 w w w w w w w w Ÿ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
7x
3x
œ
9
œ
œ
œ
œ
œ
60 s FINE
4 &4 #œ
3
œ
œ
œ
3
œ
œ
#œ
3
œ
œ
œ
3
œ
3x
Œ
? 44 w w w w w w w w Ÿ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 4 & 4 #œ
3
œ
œ
Ϫ
3
œ œ #œ nœ
4 & 4 #œ
3
œ
œ
Ϫ
3
œ œ #œ nœ
3x
3x
&4 4# œ
& 45 Œ
Œ
Œ
Œ
Œ
3
œ
œ
œ
3
œ
œ
#œ
f3 a d e
œ
œ
œ
3
œ
o
Œ
u
w ?4 w w w w 4w w w Ÿ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 4 & 4 #œ
3
œ
œ
Ϫ
3
œ œ #œ nœ
4 & 4 #œ
3
œ
Ϫ
15 x œ
3
œ œ #œ nœ
t
