Acoustical Parameters

From Inspired Acoustics Knowledge Base

Acoustical parameters are the objective measures of the acoustics in rooms.

Room impulse response representations

Nowadays, we talk about room impulse responses in the digital domain, namely a sampled and quantized impulse response, recorded with a computer or equivalent equipment.

• (Digital) Time domain (Shannon)
  • Temporal function, sample vector
  • Energy Time Curve (ETC)
  • Energy Decay Curve (EDC)
• Frequency domain (Fourier)
  • Magnitude response
  • Phase response
    • Phase delay response
    • Group delay response
• Complex frequency domain (Laplace)
  • Transfer function
• Time-frequency domain (Wigner, Gabor, etc.)
  • Short-term Fourier Transform (STFT) or spectrogram
  • Wavelet transform or scalogram
  • Other time-frequency representations
• Any-to-spatial domain
  • Density plots: some parameter or a multidimensional function plotted as the function of space (physical location).

Acoustical parameters

The acoustical parameters can be classified into the following categories, together with some examples:

• Temporal parameters
  • Initial time-delay gap (ITDG, t1)
  • Early reflections - tail boundary, ER-limit (transition time, te)
  • Reverberation time (RT60, T10, T20, T30, etc)
  • Early decay time (EDT)
  • Bass ratio (BR)
  • Treble ratio (TR)
  • Rise time (TR)
  • Inversion index (II)
  • Steepness (sigma)
  • Temporal diffusion (Delta)
• Energetic parameters (energies and energy ratios)
  • Clarity (C7, C50, C80)
  • Definition (D50, D80)
  • Strength (G, G80, GL)
  • Center time (Ts)
  • Reverberant to early sound ratio (R)
  • Hallmass, Hallabstand (H)
  • Echo Criterion (EC)
  • Spectral Density (S)
  • Early Energy Balance (EEB)
• Spatial parameters
  • Lateral Strength (GEL, GLL)
  • InterAural Cross-correlation Coefficient (IACCA, IACCE, IACCL, IACCE3, IACCL3)
  • Lateral Energy Fraction (LF, LFC, ELEF)
  • Lateral Efficiency (LE)
  • Spatial Impression (SI)
  • Subjective Spaciousness (SS)
  • Surface Diffusity Index (SDI)
  • Room Response (RR)
• Stage parameters
  • Support (ST1, ST2, STearly, STlate, STtotal)
  • Clarity on Stage (CS)
  • EDT on Podium (EDTP)
  • Early Ensemble Level (EEL)
• Quantitative Speech Intelligibility Parameters
  • Speech Transmission Index (STI, STIr, STIEL, STIPA, RaSTI)
  • Speech Intelligibility Index (SII)
  • Articulation loss of Consonants (AlCons), Privacy Index (PI)
  • Radius of distraction (rd), radius of privacy (rp)

The above mentioned parameters are not fully independent. The list of independent parameters according to Y. Ando are the following:

• Listening level (LL)
• Initial time delay gap (ITDG; Delta t1); without the ground reflecion
• Subsequent reverberation time (Tsub)
• Inter-aural cross-correlation coefficient (IACC)

Objective and subjective pairing

The following list shows the subjective acoustic impression paired to its corresponding objective acoustical parameter.

• Reverberance: EDT
• Liveness: EDT, RT
• Fullness: RT
• Loudness: G
• Clarity: C80
• Timbre: RT(f)
• Warmth: BR
• Brilliance: TR
• Stage support: ST1
• Hall response: STlate
• Spaciousness: LF, IACCE
• Apparent source width: LF (500-4000 Hz), IACCE
• Listener envelopment: LLF (125-500 Hz), IACCL
• Intimacy: LF, IACCE
• Ensemble: CS, EDTP