Up to 20 years if you have not abused headphones and concerts, the ability to perceive frequencies is maximum. Or approximately 20Hz to 20,000Hz. 1 Hertz is written Hz, = one oscillation per second.
The louder the sound, the more directional it is in space like a laser beam. That is why it is advisable to have tweeters at ear level, but treble stops quickly due to obstacles.
The lower the sound, the more it radiates in all directions and crosses many obstacles such as walls and ceilings.
A church organ can drop to 16Hz. The bass of a 26.7Hz grand piano, the electric basses are between 40 and 50Hz. The lowest frequencies are vibrations that we can pick up. Higher frequencies, if not directly audible, can influence the audible frequencies through the harmonic set. These harmonics are multiples or submultiples of the fundamental frequencies. They characterize the timbre of a voice or an instrument or a microphone.
The most common audio formats.
.MP3 called MPEG 1 and 2 layer 3 (since 1992)
The evolution of the format recently stopped, it is a compressed format. There are 56 different 56Khz qualities, enough to listen to a dictated text. 128kilo bits per second is fine for electric music or 320KBPS, the highest quality in MP3. It exists in medium quality with a variable bit rate VBR = variable bit rate. The quality of the transmission varies in real time according to the variations of the audio file.
.WMA Windows Media Audio (since 1999)
Compressed format used by Microsoft Windows software with variable quality, in some cases lower or higher than MP3. In 8 or 16 bits, sampled from 8Hz to 48KHz, mono or stereo with a data stream of 5 to 192KHz. With a quality roughly equal to MP3 128KPPS, the 96KHz WMA file takes 25% less space than MP3.
.OGG Vorbis (since 1993)
Less common format. It is a compressed audio format that comes from the free Linux environment. Slightly higher than MP3 and WMA format suitable for 8 to 48KHz 16-24 bit surround sound and transmission, with an audio data stream of 16 to 512KBPS, often 128 to 320KBPS. It exists in medium quality with a variable bit rate VBR = variable bit rate. The quality of the transmission varies in real time according to the variations of the audio file.
AAC Advanced Audio Coding (since 1997)
The compressed format allows better quality than MP3. An upgraded version HE-AAC or eAAC + (MPEG 4) is used for DAB (Digital Audio Broadcasting) digital radio transmission.
.M4a (audio) and .MP4 (audio or video)
Compressed formats. They are used for APPLE products and are of very good quality.
.WAV
It is a very good quality uncompressed format. By default, high-quality recording in dictaphone. For an audio CD (700Mo), these are 16-bit packets extracted or read 44100 times per second = 44.1KHz with a flow of 1411KBPS = Kilo bits per second. Which is much higher than the MP3 which has a 320KBPS limit.
