A BSTRA CT
Experiments were carried out concerning relationships between subjective clarity and criterion C80 in a variable acoustical room. Some discrepancies appeared and the effect of early reverberant energy was then investigated with artificial reverberation. It was found that subjective clarity could be increased by a great interspike gap (GIG).
RELATIONS BETWEEN SUBJECTIVE CLARITY AND GEOMETRICAL PARAMETERS OF ESPRO
Method
2.1.1 Physical measures
ESPRO is a parallelepipedic room (24 m long and 15 m wide) whose walls are composed of orientable trihedrals with absorptive-diffusing-reflecting sides.
The height of the ceiling is variable from 2.5 to 12.5 m. The following experiment was realized by J. Jouhaneau, J.-P. Jullien and J. D. Polack. An
TABLE 1 Definitions
Geometrical parameters of ESPRO
H, height of ceiling: high (10m), median (7.5 m), low (5 m)
A/D, ratio of absorptive to diffusing panel numbers: strong (oo), median (200%), weak (30%) P, receiver position in the room: P1 and P3 in the axis of the room, respectively at 7 and 16m from the loudspeaker line, P2 close to a lateral wall at 12m from the loudspeaker line G, absorptive panel distribution gradient, which indicates that absorptive panels are either predominantly grouped or uniformed distributed in the room (three values) R, percentage of reflecting panels (three values) Acoustic criteria C80 (dB) = 10 log ffยฐ'ยฐa p2(t) dt/S~.oap2(t) dt) C50 (dB) = 10 log (Sยฐ'ยฐ5 p2(t) dt/~p2(t) dt) S/B (dB) = 10 log (~o.o95 a(t)p2(t) dt/~.o9 s p2(t )dt) Ca(t) is a weighting function, a(0) = 1, a(0.095) = O)
Perceptive parameter
Subjective clarity was evaluated by subjects according to the following definition:
'Subjective clarity is high if sound details and attacks are well perceived. This characteristic is often designed by definition or precision. You have only to evaluate subjective clarity independently of other parameters, like tone coloration for example'
Parameters of artificial reverberation
Distribution: simulated impulse response, or this impulse response convolved with an anechoic musical sample Direct impulse: burst of white noise of 5 ms duration which simulated direct sound Spike: burst of white noise which simulated a reflection Temporal energetic barycentre computed in the first 80 ms (ms): S ยฐ'ยฐa tp2(t)dt/Sยฐo'ยฐap2(t)dt Spike time delay (ms): difference of time between spike and direct sound Spike width (ms): duration of white noise burst (narrow, 5 ms; wide, greater or equal to 10ms) Interspike gap (ms): difference of time delay between two successive spikes GIG: great interspike gap (ms): interspike gap greater than other interspike gaps