4f, 5f, etc. (where f is a specific frequency), humans tend to perceive that the pitch is f. An audible example can be found on YouTube. Software The psychoacoustic model provides for high quality lossy signal compression by describing which parts of a given digital audio signal can be removed (or aggressively compressed) safely—that is, without significant losses in the (consciously) perceived quality of the sound. It can explain how a sharp clap of the hands might seem painfully loud in a quiet library but is hardly noticeable after a car backfires on a busy, urban street. This provides great benefit to the overall compression ratio, and psychoacoustic analysis routinely leads to compressed music files that are one-tenth to one-twelfth the size of high-quality masters, but with discernibly less proportional quality loss. Such compression is a feature of nearly all modern lossy audio compression formats. Some of these formats include Dolby Digital (AC-3), MP3, Opus, Ogg Vorbis, AAC, WMA, MPEG-1 Layer II (used for digital audio broadcasting in several countries) and ATRAC, the compression used in MiniDisc and some Walkman models. Psychoacoustics is based heavily on human anatomy, especially the ear's limitations in perceiving sound as outlined previously. To summarize, these limitations are: High-frequency limit Absolute threshold of hearing Temporal masking (forward masking, backward masking) Simultaneous masking (also known as spectral masking) A compression algorithm can assign a lower priority to sounds outside the range of human hearing. By carefully shifting bits away from the unimportant components and toward the important ones, the algorithm ensures that the sounds a listener is most likely to perceive are most accurately represented. Music Psychoacoustics includes topics and studies that are relevant to music psychology and music therapy. Theorists such as Benjamin Boretz consider some of the results of psychoacoustics to be meaningful only in a musical context. Irv Teibel's Environments series LPs (1969–79) are an early example of commercially available sounds released expressly for enhancing psychological abilities. Applied psychoacoustics Psychoacoustics has long enjoyed a symbiotic relationship with computer science. Internet pioneers J. C. R. Licklider and Bob Taylor both completed graduate-level work in psychoacoustics, while BBN Technologies originally specialized in consulting on acoustics issues before it began building the first packet-switched network. Licklider wrote a paper entitled "A duplex theory of pitch perception". Psychoacoustics is applied within many fields of software development, where developers map proven and experimental mathematical patterns in digital signal