Workers exposed to noise levels of 85 dB have a permissible maximum daily average exposure of only eight hours and workers exposed to noise levels of 103 dB(A) have a permissible maximum daily average exposure of only 7.5 minutes . However, most of the participants in the sound technician group at Cultura TV and at Record TV exceeded the sound level permitted for eight hours, given that 57.3% of the workers examined in this study were working for between 6 and 12 hours per day and 13.4% were working for more than 12 hours a day in a place proven to be inappropriate for hearing (Table 2), because the sound pressure level was above the permissible daily level. Most of the participants in the sound technician group said that they had been doing that type of work for between 5 and 14.9 years (47.6%) (Table 2). Studies on different populations exposed to sound have also demonstrated inappropriate mean sound levels of between 108 and 110 dB(A) [19–30].
We considered that individuals whose audiograms presented thresholds of less than or equal to 25 dB at all the frequencies examined presented normal hearing, in accordance with the standards of the Workplace SafetyOffice.
According to Santos & Morata (1999) , factors such as gender and age have been described as worsening factors for high frequency hearing loss consistent with noise exposure. However, in our study, these possible confounding factors were controlled for, because there was no statistically significant difference between the sound technician group and control group in these respects, thus rendering the study sample homogeneous without such bias in the results (Table 1). Furthermore, the individuals in both study groups were predominantly within the age range from 25 to 35 years old. Thus, young adults predominated in our study, with a consequently lower risk of developing presbyacusis (Table 1).
There was a statistically significant difference (p = 0.009) with regard to the presence of hearing complaints between the individuals in the sound technician and control groups (Table 1). Thus, the sound technicians had more hearing complaints than did the control group, and tinnitus was the most frequently reported complaint. These results were already expected and corroborate the results from various studies carried out among musicians in street carnival bands, disc jockeys, symphony orchestra musicians and others, which have described tinnitus and dizziness as the most frequently reported complaints [19–30].
There were no statistically significant differences in music listening habits and ototoxicity exposure between the groups studied (p > 0.05) (Table 1). However, the exposure to noise during leisure activities that was most mentioned in the studies that we researched in the literature and also in our study was going to discos and using a walkman [19–30].
Tinnitus is a symptom that may be found in workers suffering from high frequency hearing loss consistent with noise exposure and, according to Ferreira Júnior (1998) , such workers may mention that they have this symptom at times of hearing rest. It was found in our study that there was a statistically significant difference in the presence of tinnitus between the sound technician and control groups (p < 0.001), i.e. there was greater reporting of tinnitus among the sound technicians (Table 1).
One example of this situation of noise exposure over a long period of time is provided by the British guitar player and singer Eric Clapton (age 62 years), who developed tinnitus after spending years of his career playing in front of sound amplifiers at high volumes. He has said that, if he could go back in time, he would ask to have lower amplifier volume during his concerts. He has reported that he constantly hears "whistles" in his ears . Another example that illustrates this situation within Brazilian popular music is provided by the vocalist of the group Jota Quest, Rogério Flausino, who is only 35 years old. In a documentary that forms part of the band's latest DVD, he reveals that he has lost 30% of his hearing because of many years living with high sound volumes . Andrade et al (2000)  confirmed a possible association between the length of time working as a musician and the incidence of hearing alterations.
The main outcome of the present study was the presence of hearing loss. With regard to this, there was a statistically significant difference (p < 0.001) between the sound technicians and controls (50% versus 10.5%, respectively) (Table 3), thus revealing that hearing loss occurred approximately five times more frequently in the sound technician group. The difference could be addressed to high sound levels.
The effect of music on sound technicians' hearing was found to be greater in the present study than in other studies such as Cunningham (2006) . This was perhaps because most of the sound technicians evaluated in the present study work or were working in open-air events, i.e. in places where the sound level is extremely higher and harmful.
Other study limitations might include residual confounding due to differences in socioeconomic status between the two study groups. This could partly explain the presence of much higher hearing loss levels among the sound technicians.
There is no effective treatment for permanent hearing loss resulting from excessive exposure to noise levels. However, this condition may generally be prevented through combined measures in programs against hearing loss (also called hearing conservation programs). Even though the efficacy of these measures (individual hearing protectors) for noise protection is determined by tests performed in laboratories, their effectiveness in preventing hearing loss due to exposure to cumulative noise depends mainly upon how regularly the workers use this protection. Studies have been demonstrating that if workers do not use hearing protectors for 100% of their working hours, the effectiveness of such devices will diminish rapidly. For example, using hearing protectors for only 90% of the time will diminish their effectiveness to less than one third of their efficacy .
85.4% of the participants in the sound technician group reported not using hearing protectors during their long working hours (Table 2). This seems to be a common phenomenon, because the majority of workers in manufacturing facilities, percussionists and musicians interviewed in other studies also reported not making use of hearing protectors. They were thus exposed to the risk of high frequency hearing loss consistent with noise exposure [16, 36–39].
A systematic review has compared the effectiveness of intervention programs versus no intervention regarding the use of hearing protectors among workers exposed to noise levels above 85 dB(A). It was concluded that there was very little evidence regarding the efficacy of long-term school programs for increasing the use of hearing protectors among school students. Furthermore, the available evidence did not show that provision of customized/standardized information to motivate the workers to use hearing protectors was more effective than general information [40, 41].
Programs for preventing hearing loss in industrial organizations have been widely defended. Occupational safety and health legislation obliges employees to have preventive measures in most countries . In Europe and the USA, verification of noise exposure is mandatory, with periodic examinations on workers exposed to certain noise levels.
Studies in the USA have indicated that the use of hearing protectors is increasing, but there is still much to be improved in this respect . Many factors have been reported as influencing the use of hearing protectors, such as the perception of risk likelihood and comfort when using the hearing protectors [35, 44–46].
Implementation of hearing conservation programs within this population is of fundamental importance not only for the well being of these individuals, but also for the enrichment of Brazilian popular music, given that it is one of the best products of our country. The perception of hearing is related to the hearing threshold and maintenance of good perception through hearing protection measures will have the consequence of developing better professionals who can work to provide even greater value for Brazilian musicians.
For this to be definitively recognized and introduced within Brazilian culture and internationally, it will continue to be highly important, as a public health measure, to develop new strategies towards increasing the use of hearing protectors.