Centre Time Ts (Clause 5.5)

Centre time represents the "centre of gravity" of the squared impulse response along the time axis:

Ts = ∫₀^∞ t · h²(t) dt / ∫₀^∞ h²(t) dt (ms)

Ts combines information from both the early and late sound field into a single number. Lower Ts values indicate that energy arrives earlier, correlating with better temporal clarity. Unlike C80 or C50, Ts does not have a fixed early/late boundary — it considers the entire time distribution.

Typical Ts Values

Space	Ts (ms)
Recording studio	10 – 30
Classroom	30 – 80
Lecture hall	60 – 120
Concert hall	80 – 200
Cathedral	150 – 400

Ts correlates inversely with C80: as reverberation increases, the centre of gravity shifts later in time, increasing Ts and decreasing clarity.

Sound Strength G (Clause 5.6)

Sound strength G quantifies the "gain" provided by the room. It is the sound pressure level at the measurement position relative to the level that would exist at 10 m distance from the same source in a free field:

G = Lp - Lp,10m (dB)

In practice, G is computed from the impulse response by comparing the total energy to the energy of the source measured at 10 m in an anechoic chamber (reference measurement):

G = 10 · log₁₀ [ ∫₀^∞ h²(t) dt / ∫₀^∞ h²₁₀(t) dt ] (dB)

G Measurement Requirements

Measuring G requires a calibrated reference: the sound power of the source must be known, or a reference impulse response at 10 m in free-field conditions must be available. This makes G the most demanding ISO 3382-1 parameter to measure correctly. In practice, many teams substitute the in-room measurement at a known short distance and apply the inverse-square law correction.

Practical Interpretation

In concert halls, G values typically range from +5 dB to +15 dB. Higher G means the room provides more support — sound is louder than it would be outdoors at the same distance. G varies significantly with receiver position: seats far from the stage have lower G. The spatial variation of G indicates coverage uniformity.

Relationship to Other Parameters

G and reverberation time are related but not interchangeable. Two halls can have similar T30 but different G values due to different volumes. The Barron revised theory predicts G from volume and T: G ≈ 10·log₁₀(T/V) + constant. Ts and G together give a more complete picture than C80 alone.

SonaVyx Implementation

The RT60 tool computes Ts from every measured impulse response. G computation requires a reference measurement, which can be provided by measuring the source at a known distance. See the INR section for quality requirements and the uncertainty reporting section for reporting results.