**2. Description of research**

#### **2.1. Audiometric tests**

The research was aimed at young people (16–25 years old) because they are the most vulnerable to hearing loss caused by frequent loud noise exposure in their own choices. Some of the people are working for the entertainment industry in professional way so they were divided into three groups reflecting their activities:


The ordinary young users of portable audio equipment were representative as the reference group for this range of age, so the total number of subjects was more than 80 people. After the interviews and giving instructions, the audibility of people was measured by the means of Maico M 53 audiometers. Audiometric tests were conducted in an anechoic chamber and in the recording studio of the Wrocław University of Science and Technology. These places meet the requirements of maximum allowable amount of background‐sound pressure level [20]. Therefore, during the test, any masking phenomenon from outer signals does not occur [20, 21]. Before the measurements all audiometers had been basically calibrated and checked aurally, also they had been calibrated subjectively in accordance with the ISO recommendations.

Threshold of hearing levels were determined by the air conduction audiometry. The measurements were carried out according to the applicable standards [20], by ascending methods and with the use of continuous sinusoidal signals. All measurement points were repeated twice in order to eliminate random errors for some of the inexperienced subjects.

#### **2.2. Detection of spectral changes of musical signals vs. TTS**

It is known from literature [14, 15, 17, 18] that the greatest effect of TTS occurs first for the range of 2–6 kHz, and this upward shift disappears after a time, usually in 24 hours, but may last as long as a week. If exposure to noise occurs repeatedly without sufficient time between exposures to allow recovery of normal hearing, threshold shift may become chronic, and eventually permanent. This is a specific danger when people who work in noisy environments are exposed to further noise afterward while driving, at home or at places of entertainment.

The facts mentioned above may reflect in an increase of hearing thresholds of the young people consuming today's music in the way that "louder means better". Of course, the higher hearing thresholds induce difficulty in collecting, understanding, and interpreting many information from the human environment which influences the sense of safety and causes the changes in the way of thinking and living together in society. It also may be interesting if the European Standard EN ISO 7029 still remains true in the light of youngsters' way of life and this aspect is the aim of presented research. According to this standard, the hearing thresholds increase with the age of a subject, starting from 0 dB, as recommended for 20‐year‐old people. The authors' research [10] showed that for young people who use to listen to the loud music via headphones the hearing thresholds have been shifted up to 6 dB. Although such hearing is still qualified as "normal" [19] (see also Section 3.1), according to the EN ISO 7029 this value of hearing threshold shift is typical for 40–50 years‐old people. The population of young people

The research was aimed at young people (16–25 years old) because they are the most vulnerable to hearing loss caused by frequent loud noise exposure in their own choices. Some of the people are working for the entertainment industry in professional way so they were divided

The ordinary young users of portable audio equipment were representative as the reference group for this range of age, so the total number of subjects was more than 80 people. After the interviews and giving instructions, the audibility of people was measured by the means of Maico M 53 audiometers. Audiometric tests were conducted in an anechoic chamber and in the recording studio of the Wrocław University of Science and Technology. These places meet the requirements of maximum allowable amount of background‐sound pressure level [20]. Therefore, during the test, any masking phenomenon from outer signals does not occur [20, 21]. Before the measurements all audiometers had been basically calibrated and checked aurally, also they had been calibrated subjectively in accordance with the ISO

with shifted threshold of hearing is growing up year‐by‐year.

**2. Description of research**

into three groups reflecting their activities:

• young classical musicians or music academy students,

• sound engineers working in recording studios.

• sound engineers of Front of House/Public Address (FOH/PA) systems and

**2.1. Audiometric tests**

170 Advances in Clinical Audiology

recommendations.

The detection of spectrum changes of musical signals was the subject of investigation in the first part of research. Sixteen subjects in the age ranging from 22 to 25 years, participated in the experiment and all of them are professional recording or reinforcement engineers. Moreover, they have experience in psychoacoustic experiments. They featured the normal hearing, that is, the absolute threshold was not more than 10 dB HL in the entire frequency range (125 Hz–16 kHz) which has been confirmed by the air conduction measurements with the Maico M53 audiometers. The threshold measurements were carried out according to the applicable standards [20, 22] by ascending stimuli methods and with the use of continuous sinusoidal signals with steps of 2 dB. All measurement points were repeated twice in order to eliminate random errors. Because the described experiment was addressed to the people working with or listening to higher sound levels of the music, the loud music as a disturbing noise typical for musical material in the studio or at the concerts, was presented without any break which reflects a typical way of sound exposure at entertainment event or studio works.

Ten musical pieces had been equalized at octave bands of 125 Hz, 1 kHz, and 8 kHz as center frequencies, with ±1.5 dB, ±3 dB and finally ±6 dB boosts of a sound material. It should be added that these frequencies as well as introduced spectral changes were chosen as typical values of correction parameters in low, medium, and high regions of frequency in mixing consoles often used in live‐reinforcement applications. The 10‐second samples have been prepared with a digital audio workstation and then recorded digitally by a TASCAM DA‐30 DAT recorder. As a trial, test stimuli samples have been presented in pairs, where the first one contained the original (nonequalized signal) and the second one, the processed signal. The time interval between samples was set at 1 s, and between pairs as 2 s. The test samples have been presented via active TLC loudspeakers and played back from DAT recorder. The subjects' task was to answer if these samples sounded the same, or not. Every combination of signal‐equalization occurred at least three times because of the statistical significance. The length of the test sequences did not exceed 5 min. The test signals contained pieces of various musical styles (pop rock, jazz, symphony, chamber music, heavy metal, etc.). The musical material used as a disturbing noise contained mostly pop and rock pieces frequently broadcasted in radio stations. The sound pressure levels in octave bands in the range of 63 Hz–4 kHz were practically constant at 87–93 dB and decreased to about 80 dB at 31 Hz and 8 kHz octave bands. These conditions of levels were maintained for both test and disturbing signals. Similar stimuli have been used in other experiments [11] as a reflection of typical distributions of sound pressure levels in musical selections performed by American rock and roll groups. This method of an experimental performance was chosen in order to limit the effect of fatigue of the subjects during the test sequence as well as the fact that listeners' attention should not be devoted on the new audio material. Also, the fixed sample sequence was used with an intention to minimize some artifacts which can appear in subjective assessment and simply refers to an accuracy increase because the attention of listeners was focused only on the noticeable changes between presented samples, without additional tasks about scaling and identifying the reason of the differences [23, 24].

In this experiment, the TTS phenomenon for the listeners was also the subject of research. The hearing thresholds were measured after every session of music exposure which enabled observation of the TTS caused by listening of loud musical signals in several periods of exposure. In this case, the thresholds of hearing were measured in the same way that at the beginning of experiment, i.e., by ascending stimuli methods and with the use of continuous sinusoidal signals with steps of 2 dB. These measurements were repeated twice.
