Tag: patcraft sound perception

Sound perception


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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.


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Perceptual encoding of audio volume

Human acoustic perception takes place in two dimensions:
frequency
and
intensity
. In the frequency domain, the human ear is able to perceive frequencies in the range of 20 to 20,000 Hz. In terms of intensity, humans perceive a dynamic range around 120 dB. Sounds of intensity greater than 90 dB. They can cause irreversible damage.

Sound is produced by the interaction of a vibrating object, a transmission medium and a receiver. In order for the sound to be perceived by the human being, the object must vibrate with a frequency between 20 Hz and 20 KHz. The vibration produces an alternative compression and rarefaction of the air that is transmitted in the form of sound waves. These waves reach the ear, where electrical stimuli are produced that the brain interprets as sounds. The sound waves are attenuated with distance and can be absorbed or reflected by the obstacles they encounter.

Sound characteristics

A sound can be described by sutone
, bell, intensity and duration
. The
tone
of a sound is directly related to frequency, although they are not synonyms. Frequency is a physical magnitude associated with any sound, while tone (high or low) is a perceptual characteristic that we only capture in periodic sounds: those with a more or less constant frequency.

From the musical point of view, when doubling the frequency of a sound, it goes to the next octave. For example, the La of the central octave of the piano has a frequency of 440 Hz., And the La of the next octave (higher), 880 Hz. In Western music, the octave is divided into 12 semitones (the twelve keys that is in every octave of a piano). To obtain the frequency of a semitone from the frequency of the previous one, one must multiply by twelfth root of 2, or what is the same: 1,05946.

The
doorbell

it is the “personality” of a sound and allows
distinguish, for example, the sound of a piano and a trumpet with equal duration, intensity and tone. Graphically, the timbre is characterized by the shape of the wave. Pure sine waves are only obtained electronically, but in nature, the sounds are more complex. The most severe vibration frequency (base frequency) is what determines the period and amplitude. The remaining frequencies, which are usually multiples of the base frequency, are the harmonics

Related to intensity is the concept of
Dynamic range
, which is the difference in decibels between the loudest and weakest sound a system can produce. In a sound device, this value indicates the difference between the maximum volume and the background noise that is emitted when there is no signal. In sound equipment of a certain quality the dynamic range ranges from 80 dB to 95 dB

File Format
•

AU
. Sun standard audio format. Poor quality but they are very common on the Internet.
•

AIFF
(Audio Interchange File Format), common on Mac. There is a version with compressed samples, AIFF-C.
•

Quicktime
It also has audio format, synchronizable and integrable with other media.
•

WAV
(Waveform) is the Windows format.
•

MP3