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Envelope shapes in classical amplitude panning. 

Envelope shapes in classical amplitude panning. 

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Amplitude-based sound spatialization without any further signal processing is still today a valid musical choice in certain contexts. This paper emphasizes the importance of the resulting envelope shapes on the single loudspeakers in common listening situations such as concert halls, where most listeners will find themselves in off-centre positions...

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... classical amplitude (or intensity) panning, transitions between adjacent loudspeakers are controlled by curves that provide a constant intensity [6]. This obviously creates a symmetrical envelope beginning at the peak of the previous loudspeaker and ending at the peak of the following one (Fig. 1). While this method works fine in a central listening position, and is also acceptable for slow movements in off-centre positions, it creates an undesirable effect of artificial interruption on the single loudspeakers when the movement becomes too ...
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... architecture. For instance, in the exhibition "Visible cities. Renzo Piano Building Workshop" (Milan, 2007), Tempo Reale realized a sound installation, entitled Memory, with 19 loudspeakers placed in a huge space where the central area was not accessible. The loudspeakers were hanging from the ceiling, forming different paths and listening areas (Fig. 10). Sound movements where mainly structured as linear trajectories of varying length. Even in a position directly underneath a loudspeaker, the transition to the adjacent speaker was clearly perceptible due to the clear attack of its envelope shape. At the same time the decay mechanism provided a smooth fadeout on the loudspeaker above ...
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... S IMULATIONS AND P ATTERNS Most contemporary research on sound spatialization focusses on the simulation of other spaces rather than the actual physical listening space. The idea of placing “an arbitrary (possibly time-varying) location within an illusory acoustic space that we hear but do not see” [1] was pioneered by John Chowning [2] and can be found nowadays, for instance, in the sophisticated “holographic” techniques of wave field synthesis [3, 4]. This concept tries to “hide” loudspeakers as much as possible from the listeners, in order to create convincing virtual sound locations. On the other hand, composers may wish to use loudspeakers as “instruments” and create interesting spatial patterns between them. This approach might be defined as pattern-oriented as opposed to simulation- oriented. The authors have developed a spatialization system which originated in live electronic productions by the Italian composer Luciano Berio. His use of electronic spatialization seems to be a natural extension of the principles of his instrumental writing, where “identical notes or similar figures pass between groups that are similar in timbre, but separated in space” [5]. In this kind of musical context, a homogeneous sound quality and sonic presence is important. Spatial movements should be achieved by purely amplitude-based methods, without altering the signals using techniques such as delay, reverberation or filtering, which are generally involved in the simulation of spatial depth. The problem of a more or less small privileged listening area (sweet spot), which characterizes simulation-oriented spatialization systems, is less relevant in a pattern-oriented approach, although patterns are usually also more evident from a central listening position. In any case, it is useful to consider not only the privileged central perspective, but to analyze what actually happens in off-centre listening positions, where the effective envelope shape applied by a spatialization II. C OMPARING algorithm S PATIALIZATION to a single loudspeaker M ETHODS located close There to the are listener some becomes advantages perceptually and disadvantages significant. of common amplitude-based spatialization techniques that will be examined by comparing one of the most simple trajectories, a regular rotation on a circular octophonic loudspeaker setup. In classical amplitude (or intensity) panning, transitions between adjacent loudspeakers are controlled by curves that provide a constant intensity [6]. This obviously creates a symmetrical envelope beginning at the peak of the previous loudspeaker and ending at the peak of the following one (Fig. 1). While this method works fine in a central listening position, and is also acceptable for slow movements in off-centre positions, it creates an undesirable effect of artificial interruption on the single loudspeakers when the movement becomes too fast. Whereas the rising envelope shape is tolerable for the listener, the fast decay and the following zero amplitude have a rather disturbing quality. Belladonna and Vidolin noted this very early [7] and implemented a generic “offset” in their spatialization system (spAAce). Instead of returning to zero amplitude, a low offset amplitude is kept continuously on all speakers (Fig. 2). An interesting analogy can be observed in an implementation of the same trajectory using Ambisonics. In this spatialization technique, a sound field is constructed from directional and omnidirectional components of a previously encoded signal [8, 9]. Ambisonics implies modulations of ampli- tude and phase on each loudspeaker. Fig. 3 shows only the amplitude variations: depending on the weight of the omnidirectional component of the encoded signal, rather “blurred” envelope shapes are generated that never actually return to zero amplitude. II. C OMPARING S PATIALIZATION M ETHODS There are some advantages and disadvantages of common amplitude-based spatialization techniques that will be examined by comparing one of the most simple trajectories, a regular rotation on a circular octophonic loudspeaker setup. In classical amplitude (or intensity) panning, transitions between adjacent loudspeakers are controlled by curves that provide a constant intensity [6]. This obviously creates a symmetrical envelope beginning at the peak of the previous loudspeaker and ending at the peak of the following one (Fig. 1). While this method works fine in a central listening position, and is also acceptable for slow movements in off-centre positions, it creates an undesirable effect of artificial interruption on the single loudspeakers when the movement becomes too fast. Whereas the rising envelope shape is tolerable for the listener, the fast decay and the following zero amplitude have a rather disturbing quality. Belladonna and Vidolin noted this very early [7] and implemented a generic “offset” in their spatialization system (spAAce). Instead of returning to zero amplitude, a low offset amplitude is kept continuously on all speakers (Fig. 2). An interesting analogy can be observed in an implementation of the same trajectory using Ambisonics. In this spatialization technique, a sound field is constructed from directional and omnidirectional components of a previously encoded signal [8, 9]. Ambisonics implies modulations of ampli- tude and phase on each loudspeaker. Fig. 3 shows only the amplitude variations: depending on the weight of the omnidirectional component of the encoded signal, rather “blurred” envelope shapes are generated that never actually return to zero amplitude. Both spAAce III. A N and A SYMMETRICAL Ambisonics A avoid PPROACH the problem of disturbing Considering envelope loudspeakers shapes at as high instruments speed on in the a pattern- single loudspeakers, oriented approach, which is envelope typical for shapes classical created amplitude by panning. spatialization But algorithms they do so can by be basically understood smoothing musically the as movement, “articulations”. and In therefore order to they achieve lose a a strong strong sense sense of of localization. localization, the This sound is due on each to the loudspeaker fact, that must in all be rather these techniques accentuated sounds at the beginning, “arrive” at whereas a certain the loudspeaker decay should in the be same relatively way long, they giving “leave” way it, smoothly generating to thus the sound symmetrical on the envelope next loudspeaker. shapes. Therefore, asymmetrical envelope shapes with a well-defined attack and a longer decay are necessary. At Tempo Reale a set of spatialization objects for use in Max/MSP was developed [10]. These are based on linear interpolations, which in a second instance are rescaled in order to obtain constant intensity. The gain factors G for n loudspeakers are multiplied by a rescaling factor R, which is calculated as: III. A N A SYMMETRICAL A PPROACH Considering loudspeakers as instruments in a pattern- oriented approach, envelope shapes created by spatialization algorithms can be understood musically as “articulations”. In order to achieve a strong sense of localization, the sound on each loudspeaker must be rather accentuated at the beginning, whereas the decay should be relatively long, giving way smoothly to the sound on the next loudspeaker. Therefore, asymmetrical envelope shapes with a well-defined attack and a longer decay are necessary. At Tempo Reale a set of spatialization objects for use in Max/MSP was developed [10]. These are based on linear interpolations, which in a second instance are rescaled in order to obtain constant intensity. The gain ...
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... S IMULATIONS AND P ATTERNS Most contemporary research on sound spatialization focusses on the simulation of other spaces rather than the actual physical listening space. The idea of placing “an arbitrary (possibly time-varying) location within an illusory acoustic space that we hear but do not see” [1] was pioneered by John Chowning [2] and can be found nowadays, for instance, in the sophisticated “holographic” techniques of wave field synthesis [3, 4]. This concept tries to “hide” loudspeakers as much as possible from the listeners, in order to create convincing virtual sound locations. On the other hand, composers may wish to use loudspeakers as “instruments” and create interesting spatial patterns between them. This approach might be defined as pattern-oriented as opposed to simulation- oriented. The authors have developed a spatialization system which originated in live electronic productions by the Italian composer Luciano Berio. His use of electronic spatialization seems to be a natural extension of the principles of his instrumental writing, where “identical notes or similar figures pass between groups that are similar in timbre, but separated in space” [5]. In this kind of musical context, a homogeneous sound quality and sonic presence is important. Spatial movements should be achieved by purely amplitude-based methods, without altering the signals using techniques such as delay, reverberation or filtering, which are generally involved in the simulation of spatial depth. The problem of a more or less small privileged listening area (sweet spot), which characterizes simulation-oriented spatialization systems, is less relevant in a pattern-oriented approach, although patterns are usually also more evident from a central listening position. In any case, it is useful to consider not only the privileged central perspective, but to analyze what actually happens in off-centre listening positions, where the effective envelope shape applied by a spatialization II. C OMPARING algorithm S PATIALIZATION to a single loudspeaker M ETHODS located close There to the are listener some becomes advantages perceptually and disadvantages significant. of common amplitude-based spatialization techniques that will be examined by comparing one of the most simple trajectories, a regular rotation on a circular octophonic loudspeaker setup. In classical amplitude (or intensity) panning, transitions between adjacent loudspeakers are controlled by curves that provide a constant intensity [6]. This obviously creates a symmetrical envelope beginning at the peak of the previous loudspeaker and ending at the peak of the following one (Fig. 1). While this method works fine in a central listening position, and is also acceptable for slow movements in off-centre positions, it creates an undesirable effect of artificial interruption on the single loudspeakers when the movement becomes too fast. Whereas the rising envelope shape is tolerable for the listener, the fast decay and the following zero amplitude have a rather disturbing quality. Belladonna and Vidolin noted this very early [7] and implemented a generic “offset” in their spatialization system (spAAce). Instead of returning to zero amplitude, a low offset amplitude is kept continuously on all speakers (Fig. 2). An interesting analogy can be observed in an implementation of the same trajectory using Ambisonics. In this spatialization technique, a sound field is constructed from directional and omnidirectional components of a previously encoded signal [8, 9]. Ambisonics implies modulations of ampli- tude and phase on each loudspeaker. Fig. 3 shows only the amplitude variations: depending on the weight of the omnidirectional component of the encoded signal, rather “blurred” envelope shapes are generated that never actually return to zero amplitude. II. C OMPARING S PATIALIZATION M ETHODS There are some advantages and disadvantages of common amplitude-based spatialization techniques that will be examined by comparing one of the most simple trajectories, a regular rotation on a circular octophonic loudspeaker setup. In classical amplitude (or intensity) panning, transitions between adjacent loudspeakers are controlled by curves that provide a constant intensity [6]. This obviously creates a symmetrical envelope beginning at the peak of the previous loudspeaker and ending at the peak of the following one (Fig. 1). While this method works fine in a central listening position, and is also acceptable for slow movements in off-centre positions, it creates an undesirable effect of artificial interruption on the single loudspeakers when the movement becomes too fast. Whereas the rising envelope shape is tolerable for the listener, the fast decay and the following zero amplitude have a rather disturbing quality. Belladonna and Vidolin noted this very early [7] and implemented a generic “offset” in their spatialization system (spAAce). Instead of returning to zero amplitude, a low offset amplitude is kept continuously on all speakers (Fig. 2). An interesting analogy can be observed in an implementation of the same trajectory using Ambisonics. In this spatialization technique, a sound field is constructed from directional and omnidirectional components of a previously encoded signal [8, 9]. Ambisonics implies modulations of ampli- tude and phase on each loudspeaker. Fig. 3 shows only the amplitude variations: depending on the weight of the omnidirectional component of the encoded signal, rather “blurred” envelope shapes are generated that never actually return to zero amplitude. Both spAAce III. A N and A SYMMETRICAL Ambisonics A avoid PPROACH the problem of disturbing Considering envelope loudspeakers shapes at as high instruments speed on in the a pattern- single loudspeakers, oriented approach, which is envelope typical for shapes classical created amplitude by panning. spatialization But algorithms they do so can by be basically understood smoothing musically the as movement, “articulations”. and In therefore order to they achieve lose a a strong strong sense sense of of localization. localization, the This sound is due on each to the loudspeaker fact, that must in all be rather these techniques accentuated sounds at the beginning, “arrive” at whereas a certain the loudspeaker decay should in the be same relatively way long, they giving “leave” way it, smoothly generating to thus the sound symmetrical on the envelope next loudspeaker. shapes. Therefore, asymmetrical envelope shapes with a well-defined attack and a longer decay are necessary. At Tempo Reale a set of spatialization objects for use in Max/MSP was developed [10]. These are based on linear interpolations, which in a second instance are rescaled in order to obtain constant intensity. The gain factors G for n loudspeakers are multiplied by a rescaling factor R, which is calculated as: III. A N A SYMMETRICAL A PPROACH Considering loudspeakers as instruments in a pattern- oriented approach, envelope shapes created by spatialization algorithms can be understood musically as “articulations”. In order to achieve a strong sense of localization, the sound on each loudspeaker must be rather accentuated at the beginning, whereas the decay should be relatively long, giving way smoothly to the sound on the next loudspeaker. Therefore, asymmetrical envelope shapes with a well-defined attack and a longer decay are necessary. At Tempo Reale a set of spatialization objects for use in Max/MSP was developed [10]. These are based on linear interpolations, which in a second instance are rescaled in order to obtain constant intensity. The gain factors G for n loudspeakers are multiplied by a rescaling factor R, which is calculated as: For efficiency reasons, R is not calculated at sampling rate, but only once for each MSP signal vector (which can be reduced to a single sample in the current MSP version). Within each signal vector, the interpolation is linear. For basic transitions between two loudspeakers, this generates a light S-like curve which very gradually rises/decays near the extreme values, whereas it is relatively steep at the centre (Fig. 4). From a listening position close to a loudspeaker, this curve is often preferable to the standard square-root or sinusoidal functions used in stereo panning, which are both very steep near zero. In the Tempo Reale spatialization system, movements are generated by scheduled sequences of lists representing gain values. The interpolation times can be defined individually for each list. Loudspeaker patterns are usually described by pseudo-binary gain values, using “1.” for the active and “0.” for the non-active speakers. If a pattern has more than one active loudspeaker at the same time, the gain factors are automatically rescaled as described above: a pseudo-binary pattern such as (1. 0. 1.) would generate the effective gain factors (0.71 0. 0.71). Actually, it is possible to choose arbitrary lists of gain factors, as they only represent proportions. A rotation is simply generated by a sequence of lists scheduled at regular intervals (Table I). It is then possible to create asymmetrical envelope shapes by defining a decay factor for successive loudspeaker configurations, producing a sort of “shadow” of the previous configurations. For each new loudspeaker configuration in Table II, the previous gain values are multiplied ...