Music to your ear (Tia liao jing song)


Sound Recording


Sound recording is the process of converting pressure waves in air (sound) into electric

signals for storage as magnetic or physical patterns in a medium such as magnetic tape,

vinyl record, or compact disc. In analog recording, a copy (analog) of the continuous sound

wave is created in the recording medium. Digital recording converts the continuous wave

into binary code of discrete pulses.

During recording , sound waves from a traditional instrument or voice must be converted

into an electric signal by a microphone, while electronic instruments, such as synthesizers,

can produce an electric signal directly. An analog electric signal is theoretically an exact copy

of the original sound wave, while digital code is only a sampled approximation. However,

digital audio has many practical advantages. Digital coding systems are designed to carry

information in addition to sound , such as error-correction data. In addition, digital copies

are identical to digital originals, which means that tracks can be copied repeatedly without


June 17, 2020 3:15 PM


Sound reproduction (Part 1 : DML (Distributed mode loudspeakers)


DML built-in wall panel :


The latest flat-speaker technology called distributed mode loudspeakers (DML),

uses an extremely stiff, thin panel vibrates in a complex way, unlike in a

conventional speaker, where a cone moves in and out like a priston. DML units

do not need an enclosure (box) , and they fill a room more evenly with sound

than conventional speakers. They can be made from various materials, even glass,

incorporating into walls and ceiling shown below picture.

Important note : Though it looks nice to have DML built-in wall but the downside could causes

                your wall paint to fall off due to long-term vibration. It will be best to have

                a flat box DML instead.

                Also, DML excitor which cost $19 a piece isn't good enough to have the best

                sound effect . You need to add a "woofer" to enhance the base with DML

                excitors. Excitor is just a "tuner" or "tweeter" which is a high frequency wave .

                Do Not waste $2,000 to $4,000 to purchase a DML .

                It only cost $19 with very POOR sound effect.

June 17, 2020 3:23 PM


Sound Reproduction (Part 2 : Speakers )


Most hifi speaker unit use two moving-coil driver units ; a "tweeter" for high frequencies and

a "woofer" for low frequencies. They are enclosed within specially designed cabinets that

incorporate damping material to absorb unwanted vibrations. An alternating electrical current

from the amplifier that represents the sound signal is sent to a crossover circuit in the cabinet .

This sends high frequencies to the tweeter and low frequencies to the woofer. The varying

electrical signals cause the driver unit's coil to move, creating varying pressure (sound) waves.

Moving-coil speaker :


                    A moving-coil speaker converts electrical currents into sound

                    through the magnetization of a wire coil connected to a flexible


June 17, 2020 3:24 PM


Sound Reproduction (Part 3 : Record player cartridge )


Reproduction of recorded sound requires a media player to convert the physical or

magnetic patterns on the recorded media into an electric signal, an amplifier to boost

the signal from the player , and speakers to convert the signal into sound waves.

If the recording medium is digital , a digital/analog converter is needed to change the

signal into analog form before it can be amplified.

Record player cartridge :


                      A vinyl record stores the two channels of a stereo sound signal

as waveline contours in the walls of a spiral groove. A cartridge at the end of the record

player tonearm detects the contour variations with a diamond-tipped stylus, which moves in

two perpendicular directions as it follows the inner and outer groove walls. The movements

of the stylus cause an attached magnet to move within two sets of coils, inducing separate

electric signals in them for the left and right channels. Some cartridge use a moving coil and

fixed magnets instead.

June 17, 2020 3:25 PM


Sound Reproduction (Part 4 : Compact disc )


Ideally, sound reproduction equipment recreates the sound exactly as originally

recorded. An amplifier must boost the level of the electric signal from the record ,

tape, or CD player without introducing unpleasant distortion. Most amplifiers

accomplish this using transistors, but amplifiers based on older vacuum tube

technology are prized by some for the "warmth: of their sound. The final

component in the reproduction chain is the loudspeaker. Speakers are transducers.

They convert electric energy into sound energy, and work like microphone in reverse.

Most speakers use moving-coil technology. "Flat" speaker designs were once usually

based on electrostatic technology and operated like condensor microphones in reverse,

but the latest flat designs use a new "distributed mode" speaker technology.

Compact disc :


               The compact disc is a 5 in. (12 cam) diameter plastic disk that can hold

approximately 74 minutes of 16-bit stereo sound, sampled at 44.1 kHz. The sound data is

stored in the form of about 3 billion "pits: in a single spiral track that starts at the center.

A typical pit is 1/40,000 in (1 micrometer) long.

CD player :


           Information is stored on a CD as a series of pits. Pits and lands (the areas in

between) represent the digital sound data. In the player, a laser beam is focused on the

track from beneath the disc and reflected back to a detector. The varying intensity of this

light (caused by the pattern of pits and bumps) is converted into an audio signal.

June 17, 2020 3:27 PM