Room acoustics

Under Room acoustics all parameters from ISO 3382-1 can be determined. The evaluation is done in two steps. At first the preprocessing needs to be performed by the Room acoustics preprocessing menu. Here all parameters are calculated and deposited in the file. Upon completion of the processing, the Room Acoustics Info window is launched automatically:

Here only those quantities are displayed, which have been activated in the Select/Select parameters submenu:

Exporting the table values can be performed by copy & paste, or the results can be written directly into Excel tables or ASCII files via Select/Show export options: Table export

In addition to the room acoustic single number values some further information can be displayed in the table:

  • Channel tag: shows the original channel assignment after the frequency band filtering. In the example shown above the original file contained 2 channels; filtering in 7 octave bands produces 14 channels with the corresponding band centre frequencies
  • fm nom. [Hz]: nominal band centre frequency after filtering
  • fm [Hz]: exact band centre frequency
  • Start [ms]: if start detect was activated in the Room acoustics preprocessing, the starting time for the evaluation of each channel is displayed here. If start detect was not activate, the start of the evaluation region is displayed, which was selected in the Room acoustics preprocessing under Region.
  • End [ms]: if end detect was activated in the Room acoustics preprocessing, the end time for the evaluation of each channel is displayed here. If end detect was not active, the end of the evaluation region is displayed, which was selected in the Room acoustics preprocessing under Region.
  • Noise [dB]: noise floor in dB
  • SNR [dB]: ratio of peak level of the impulse response to noise floor

Room acoustic single number values

All calculation formulae implemented in WinMF are taken over from ISO 3382-1:2009. All quantities are based on one or several measured impulse responses. For some parameters measurements using 2 microphones (omnidirectional and figure-of-eight characteristics) are required. Furthermore some evaluations require additional measurement of the sound source under free-field conditions.

Annex A - Auditorium measures

  • Sound strength G: the logarithmic ratio of sound energy of an impulse response measured by an omnidirectional microphone in the audience area and the energy of the impulse response of the same sound source under free-field conditions measured at a distance of 10m. The analysis in WinMF assumes, that the odd-numbered channels contain the impulse responses from the audience area; the even-numbered channels contain the corresponding measurements with the sound source under free-field conditions. As generally these measurements take place locally and temporally separated, it is favourable to perform the single measurements in terms of frequency responses with the same settings. Thereby it can be ensured, that the impulse responses have correct amplitudes, irrespective of the actual measuring voltage. If it is not possible to measure at a distance of 10m, in most cases smaller distances should be acceptable, as long as a sufficient distance to the near-field to far-field threshold of the sound source is maintained. Furthermore it should be noted that the free-field measurement of the sound source shall be an energetic average around the source in angular intervals of 12.5°, in order to obtain an average of the emitted power.
  • L_pE, L_pE10: sound energy level of the impulse responses. Both quantities are partial results of the sound strength determination. L_pE is the energy level of the impulse response(s) in the audience area (odd-numbered channel(s)), L_pE10 is the energy level of the impulse response(s) measured at 10m under free-field conditions (even-numbered channel(s)). G is calculated by: G = L_pE - L_pE10.
  • Clarity C50, C80: logarithmic ratio of early-arriving energy to late-arriving energy. C50 uses a limit of 50ms for the early energy, C80 evaluates a range of 0-80ms. The measurement is performed using an omnidirectional microphone.
  • Definition D50, D80: ratio in per cent of early-arriving energy to total energy of the impulse response. D50 uses a limit of 50ms for the early energy, D80 evaluates a range of 0-80ms. The measurement is performed using an omnidirectional microphone.
  • Centre time Ts (Gravity): energetic centre point of impulse response
  • Early lateral fraction J_LF: logarithmic ratio of energy in the range from 5ms to 80ms of the impulse response measured by the figure-of-eight microphone to the energy in the range of 0 - 80ms of the impulse response measured by the omnidirectional microphone. For calculation in WinMF the impulse responses of the figure-of-eight microphones need to be present in the odd-numbered channels, the omnidirectional impulse responses shall be assigned to the even-numbered channels. For the measurement the lobes of the figure-of-eight microphone shall be aligned perpendicular to the direction of the sound source.
  • Early lateral fraction J_LFC (cosine energy directivity): somewhat different calculation, leading to a cosine directivity regarding the direction of arriving sound energy. Channel assignment and positioning of microphones are identical to J_LF.
  • Late lateral energy L_J: Channel assignment and positioning of microphones are identical to measurement of early lateral fraction, but here the energy from the figure-of-eight microphone is evaluated starting from 80ms, the impulse response of the omnidirectional microphones is integrated over the entire range.

Annex B - Binaural auditorium measures

For all binaural measurements the impulse responses of the left ear need to be assigned to the odd-numbered channels, the right ear impulse responses are put on even-numbered channels. Basis for the binaural measures is the normalised inter-aural cross correlation function (IACF), calculated with an integration interval t1 to t2. The inter-aural cross correlation coefficient IACC_t1,t2 is derived as the maximum magnitude of the IACF in an interval from -1ms to 1ms. WinMF provides three integration intervals (with the starting time referring to the start of the impulse response, see Room acoustics preprocessing).

  • IACC_t1:t2: arbitrary limits, to be defined under processing options in the Room acoustics preprocessing
  • IACC_0-80ms: fixed integration interval from 0 to 80ms for evaluating early reflections
  • IACC_80ms-: fixed integration interval from 80ms to the end of the impulse response for evaluating decay

Annex C - Stage measures

For determination of early and late support impulse responses measured by omnidirectional microphones are analysed. Starting times refer to the starting time detected or defined in the Room acoustics preprocessing.

  • ST_Early (Early support): logarithmic ratio of energy between 20ms and 100ms to energy in the range of 0-10ms
  • ST_Late (Late support): logarithmic ratio of energy between 100ms and 1000ms to energy in the range of 0-10ms