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  Time-dependent loudness – ISO 532-1
HEAD Press Release Herzogenrath (Germany), October 16, 2014
Time-dependent loudness – ISO 532-1
A new international standard for the determination of time-dependent loudness is soon to be published as a revision of ISO 532 B. The future ISO 532‑1 standard is based on the DIN 45631/A1 standard for determining both stationary and time-variable noise according to Zwicker.
In the new standard, the calculation method and the implementation of the algorithm are described in full detail, thus avoiding any uncertainty regarding the practical implementation. Since the new standard fully complies with the criteria of DIN 45631/A1, it offers better continuity and comparability than earlier calculations. Furthermore, ISO 532 A (loudness according to Stevens) is replaced by ISO 532-2. In this case, the standard is based on the American ANSI S3.4-2007 standard for calculating stationary loudness according to Moore and Glasberg.
On our web site you can download a tool that you can use to try and apply the new ISO 532-1 standard.
Calculation of loudness of stationary and time varying sounds
The source code for the loudness calculation procedure will be published in ISO 532-1 Annex A.3. Here, the executable for Microsoft Windows OS is provided together with a graphical user interface and some test signals.
1. ISO_532-1.exe:
The compiled version of the program code as a command line application.
    read more (italic phrases are commands)
  ISO_532-1 Stationary <F|D> <input file> [<ref. file> <ref. level>] <time skip value>
  Stationary loudness with given WAVE input file with 32-bit float format for free (F) or diffuse (D) field.
Do not consider first <time skip value> seconds for calculating third octave levels,
e.g. <time skip value> = 0,2.
If <input file> is in 16-bit integer format, a reference file <ref. file> and a reference level <ref. level> (dB rms) must be provided. Specific loudness (average) is written into a CSV-file.
  ISO_532-1 Stationary_Levels <F|D> <input file>
  Stationary loudness with given third octave levels from input file for free (F) or diffuse (D) field.
Specific loudness (average) is written into a CSV-file.
  ISO_532-1 Stationary_Levels <F|D> <third octave levels>
  Stationary loudness with given third octave levels (28 levels) for free (F) or diffuse (D) field.
Separate third octave levels must be separated by a colon with no white space.
Specific loudness (average) is written into a CSV-file.
  ISO_532-1 Time_varying <F|D> <input file> [ <ref. file> <ref. level> ]
  Time varying loudness with given WAVE input file with 32-bit float format for free (F) or diffuse (D) field.
Specific loudness vs. bark and time function is written into a CSV-file.
If <input file> is in 16-bit integer format, a reference file <ref. file> and a reference level <ref. level> (dB rms) must be provided.
Input as WAVE files
Supported sound files are 16-bit integer or 32-bit float WAVE files (correct sound pressure values, no normalized data) containing one channel. Sampling rates must be 32 kHz, 44,1 kHz or 48 kHz. Stationary signals should be longer than <time skip value> seconds (start of signal not used for level calculation).
Input as third octave levels
For level input, a text file format is supported with two colon separated columns. The first column lists the mid frequencies of the frequency bands and the second column the corresponding third octave levels. White space and empty lines as well as lines starting with # are ignored.
(see example file: testlevels.txt in the download section)
2. ISO_532-1_GUI.exe:
A graphical user interface (GUI) for easier executing ISO_532-1.exe with the appropriate parameters. This program depends on ISO_532-1.exe, which must be present in the same directory. In the following, some examples of how to use ISO_532-1_GUI.exe are given.
    read more
Starting ISO_532-1_GUI.exe shows the following GUI (Figure 1).
Figure 1
Graphical user interface (GUI) for loudness calculation at start-up.
The program can calculate the loudness either from third octave band sound pressure levels (in dB) or from a WAVE audio file. To select one of the two input methods activate the corresponding radio button (either “Input levels” or “Input audio signal”). By default “Input audio signal” is activated. In this case an input WAVE file may be selected by pressing the button ‘…’ to the right of the “Input WAVE file” input field (Figure 1). The file may contain only one channel. Sampling rates of 32 kHz, 44,1 kHz, and 48 kHz are supported. The data format can be 16-bit integer or 32-bit float format (correct sound pressure values, no normalized data). In case of 16-bit integer format, an appropriate calibration file and the corresponding calibration value must be given as shown in Figure 2 (see input fields “Calibration WAVE file” and “Calibration level” (dB rms)).
Figure 2
Graphical user interface (GUI) for loudness calculation (example for a 16-bit integer WAVE file, calibration file and level are given), method for stationary sounds and free sound field chosen.
Then the calculation method must be chosen. For the method for stationary sounds, the calculation can be started at a specified time T (0,0 s ≤ T ≤ 1,0 s, in the example 0,2 s) to avoid transient effects due to third-octave filtering. The specific loudness values (average) are written to a CSV-file with a resolution of 0,1 Bark. For the method for time varying sounds, a CSV-files containing the loudness vs. time function and a second CSV-file containing the specific loudness vs. Bark and time function are generated. The time resolution is 2 ms.
Finally, the sound field must be specified as free or diffuse field. The calculation is started by pressing the ‘Run’ button. For the test file of a 1 kHz tone with a level of 40 dB, setting the loudness method to “Stationary“, and the sound field to “Free”, a loudness of 1 sone and 40 phon respectively should be shown in a box (Figure 3).
 
Figure 3
Box showing the results for the example of a 1 kHz tone with a level of 40 dB, method for stationary sounds and free sound field chosen.
In case of 32-bit float format, no calibration file and calibration level are needed. Only the method and sound field must be selected (Figure 4).
Figure 4
Graphical user interface (GUI) for loudness calculation (example for a 32-bit float WAVE file, calibration file and level are not demanded), method for time varying sounds and free sound field chosen.
When the method for time varying sounds is chosen, after pressing the ‘Run’ button the calculation is started and at completion the following message specifying the output files is shown (Figure 5).
 
Figure 5
Box showing the names of the output files with results for the example of a sweep signal (20 Hz – 20 kHz) with a level of 80 dB (method for time varying sounds).
When “Input levels” is selected as input method, the levels of the third octave bands with the given centre frequencies can be input directly (Figure 6). In this mode the loudness method for stationary signals is preselected. Alternatively to manually inputting the values into the input fields, the values can be loaded from a file by pressing the “…” button on the right of the level input fields and selecting the input file with the format described above (an example file “testlevels.txt” can be found in the download section).
Figure 6
Graphical user interface (GUI) for loudness calculation (example for direct input of third octave levels and free sound field chosen).
This software is made available with permission of the authors (HEAD acoustics GmbH, Germany).
3. Test signals
Test signals are provided as WAVE audio files in 16-bit integer and 32-bit float format together with the corresponding results (loudness and specific loudness) in CSV-files.
Calculation of loudness of stationary and time varying sounds (ISO 532-1)
Program and test signals
Download now  
For immediate release. In case of publication please notify and/or provide printed copy!
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