frequency lowering

background and aim: it has been several decades since the technology of frequency lowering (fl) has been proposed. however, primary research has revealed no benefits regarding the use of this technique. currently, new methods for fl and improvement of perception of speech and fricative sounds have led to the application of these methods by numerous companies to produce hearing aids. in this study, through reviewing the findings of recent studies we introduced several fl techniques used in various companies. recent findings: results of studies conducted since the year 2000 on fl technology suggested that this technology could be used to improve speech perception in cases of high frequency hearing loss. today, the majority of hearing aid manufacturers use different fl methods. conclusion: while the setting principles of fl methods are still vague, improved hearing of fricative sounds has been associated with increased use of this technique by researchers. fl technique has its own benefits and setbacks, understanding of which would facilitate the use of fl techniques and adjustment of hearing aids for hearing-impaired individuals.