Audio Output Devices Review
Audio signal input & output:
To get started let’s find out what the sound generally is. Sound – an oscillation (waves) propagating in the air or other medium from the source of vibrations in all directions. When the waves reach your ears, located in it sensors perceive this vibration, and you hear the sound.
Every sound is characterized by the frequency and intensity (loudness).
Frequency – the number of sound vibrations per second, as measured in hertz (Hz). One cycle (period) – this is one source of traffic fluctuations (there and back). The higher the frequency, the higher the pitch.
The human ear perceives only a small range of frequencies. Very few people hear sounds below 16 Hz and above 20 kHz (1 kHz = 1000 Hz). Sound frequency of the lowest note on a piano is 27 Hz, and the highest – a little more than 4 kHz. The highest audio frequency that can transmit FM-radio broadcasting station – 15 kHz.
The sound volume is determined by the amplitude of the oscillations. The amplitude of the sound waves depends primarily on the power source. For example, a piano string with a weak impact on the key sounds quiet as its range of oscillation is small. If you strike a key harder, the amplitude of the vibrations of the string increases. Loudness of sound is measured in decibels (dB). The rustle of leaves, for example, has a volume of about 20 dB, the usual street noise – 70 dB, and close thunderclap – 120 dB.
Currently, audio output devices have become an integral part of each PC. During the competition produced a versatile, widely supported standard for audio software and hardware. Sound devices have evolved from expensive exotic additions to the usual part of virtually any configuration.
Multimedia systems began with the sound, which is perceived regardless of the image, without prejudice to the perception of the displayed information, and with good quality even adds to it and increases the susceptibility of the user who has a profound psychological impact on the operator sets the mood. Sound is an additional way to communicate on the ground and the background processes, such as reproduction of speech gives an idea of ??the speaker’s identity, helps to understand the pronunciation of words.
But the sound (audio or acoustic) information has independent significance. We can identify three areas in the use of sonic possibilities of audio output device:
1. Household multimedia systems using PC sound capabilities in training, enrichment programs (teaching reading, pronunciation, music) in encyclopedias and reference books (household-medicine, the schedule of buses, trains, airplanes, weather, repertory theaters, etc.). In domestic systems, the use of such music editors, as Skream Tracker, allows you to move to a qualitatively new level of use of audio – from passive acceptance to active work of music with pieces of music with no musical education, the implementation of color music on the PC screen;
2. Multimedia business applications use sound for the following purposes: training (professional training systems: foreign language, voice recognition birds, recognition of a heart murmur, and other organs, in education radiotelegraph), presentation (ie demonstration of the goods by the computer), holding dubbed video and teleconferencing, voice mail, automatic transcriptions (speech perception and its translation in text form), use of the user’s voice for the protection (electronic locks, access to software and information in the computer, to bank safes, etc.);
3. Professional multimedia system – is the means of production dubbed movies, home music studio (music editors like Skream Tracker, Whacker Tracker and others can strum tune the software to perform its processing (change the pitch, sound duration, type of tool velocity-key release, synthesized sound effects, play or record on a standard recording devices).
1. Digital Representation of Audio Signals
The original form of the audio signal – a continuous change in the amplitude over time – is represented in digital form by means of cross-time sampling and level. Along with the time-sampled amplitude is performed – measurement of the instantaneous amplitude values ??and their representation in the form of numerical values. The resulting stream of numbers (a series of binary numbers) is called pulse code modulation – PCM
Line in, Mic in – line and microphone inputs
Aux: the signal from this input bypasses all devices and immediately goes to the output.
CD in use for the CD-ROM.
All the mini-Jack connector
On the rear panel there is a 15-pin midi / joystick port is used for connecting synthesizers, keyboards or a joystick.
All signals from an external audio device receives the input mixer, it is used for amplification.
ADC – analog-to-digital converter. Measures the amplitude of the input signal and encodes ratio.
DAC – digital-to-analog converter. Replaces codes converts an analog signal.
DSP-signal processor controls the exchange of data with the rest of the computer devices via the ISA or PCI
Synthesizer – an imitation of musical instruments.
FM (Frequency Modulation – Frequency Modulation) synthesis to maintain compatibility with Sound Blaster.
Wave Table-synthesizer for producing high-quality sound.
RAM – RAM is used to download audio
ROM – read-only memory, it stores samples of sound
The basic formats
1) MIDI (Musical Instrument Digital Interface) (30-150 KB). Allows you to use the resources of the processor and memory.
2) WAV (30-50 MB). Representation of sound in the form in which it is – in the form of a digital representation of the original sound vibrations or sound waves. Allows you to work with the sounds of any kind, of any form and duration.
3) Mp3 – the most complex scheme of family Mpeg – requires more time spent on coding and better sound quality. The most common format for storing music.
2. Devices for input and output of audio information (sound cards)
2.1 Audio Output Device
- Electro-acoustic audio output device for speech, music and more.
By the method of sound radiation are distinguished:
- Horn (the most common, because have greater impact);
Loudspeakers – audio output device, used to listening to music and sounds. Come in different sizes and capacities. The easiest option – 2 columns, but there are kits consisting of a large number of speakers.
Loudspeaker system - a audio output device for audio playback. An electrical signal transducer to the sound pressure.
speaker system can be single-sideband (one broadband transmitter, such as the dynamic head) and multiband (two or more heads, each of which generates sound pressure in its frequency band.)
Speakers have good or improved magnetic shield structure of the magnetic system.
There are two types of speakers:
- Active (built-in amplifier, requires extra power supply, volume and tone controls);
- Passive (small capacity).
PC speaker - the simplest audio output device, is used in IBM PC and compatible computers . Sounds pretty rough and can irritate some users. Before the advent of inexpensive sound cards was the main speaker audio playback device.
Currently, PC speaker is a staff unit IBM PC-compatible computers, and is mainly used for signaling errors, particularly during POST .Some programs ( Skype ) can be set to sound output from the speaker – it is convenient, when connected to the sound card headphones(the default is not worn).
There are two ways to control the speaker:
- Programmable timer generates a square wave of a given frequency sound without the involvement of the CPU . It lets you play simpleMonophonic tones. If the program crashed when playing audio, the timer continued to work, producing a single note while the computer is rebooted;
- Direct control of the membrane through the port
61h in increments of 1 bit. By applying a high frequency is 0, 1, by means of pulse-width modulation can be synthesized inferior digitized sound – however, due to the substantial use of the CPU. All such programs do not work in multi-tasking operating systems.
Classification of earphones:
1. Mode of transmission of sound:
- Wire - audio output device connected to the power cord, so they can maximize the sound quality (respectively with professional direction headphones are specific to this type);
- Wireless - audio output device connected to a source over a wireless channel of any type - radio , infrared , Bluetooth. Mobile, but are attached to the base (emitter) and the limited range defined by the capacity of the radiator. Have a lower sound quality compared to wired, by the process ofmodulation encoding, decoding, necessary for signal transmission from the transmitter to the receiver in the headphones.
2. By design type (type):
- Plug-in (common name - “ear” ) – are inserted into the ear ;
- intracanal (common name – “gag”) – are inserted into the ear canal ;
- Overhead – are superimposed on the ear;
- Or a full-size monitor - fully embrace the ear.
3. By Type of fastening:
- Headband – Headphones vertical shackle that connects the two cups of headphones;
- Occipital headband – connects the two parts of headphones, but it is located on the back of his head. The main mechanical load is directed to the ears;
- Mounting ears – usually this type of earphones are fixed to the ears with zaushiny or clips;
- No attachments – they hold only by ear pads that are in the ear passage .
4. By the method of connecting cable:
- Double sided – the connecting cable is supplied to each of the headphone cups;
- One-sided – the connecting cable is supplied to only one cup headphones, a second outlet connected the wires from the first, is often the one hidden in the bow.
5. According to the laser design:
- Dynamic - audio output device using electrodynamic principle of transformation. The most common type of headphones. Structurally earphone represents emitter or membrane which is attached to the wire coil in the magnetic field of the permanent magnet. If therethrough keep the alternating current, the magnetic field generated by the coil would interact with the magnetic field of the permanent magnet, whereby the membrane will move repeating form electrical audio signal (see “ Speaker ”). Electrodynamic way to convert the signal has many drawbacks and limitations, but constantly improving the design of these headphones and new materials allow to achieve very high quality of sound;
- with balanced armature - the main part is the U-shaped anchor of a ferromagnetic alloy. Colloquially they are often called “reinforcement” because of the consonance of English words armature (anchor) Russian valves;
- Electrostatic – use a very thin membrane disposed between the two electrodes. The cost of these headphones are usually high, but they show very high sensitivity and high fidelity sound reproduction. Disadvantage – they can not be directly connected to a standard headphone output, so to them in a special bundle includes a docking station;
- Isodynamic – a thin film membrane, coated with a metal wirings enclosed in an array of bar magnets and ranges therebetween;
- Orthodinamic – on the principle isodynamic are similar, but the membrane and the magnets have a circular shape.
6. By type of acoustic design:
- Open – partly passed outside sounds, which allows for a more natural sound. Many students say the sound of open headphones as more transparent and natural sound than the closed headphones. In addition, an open acoustic design does not make you auditory “cut off” from the outside world. However, the high level of ambient noise in open headphones sound is difficult to hear. Also open headphones working at a high volume may hinder others. Do not create pressure on the inner ear ;
- Semi-open (or semi-open) – have many of the properties of open headphones, but offer decent sound insulation;
- Closed – do not miss out external noise and provides maximum sound isolation so you can use them in noisy environments as well as in cases when you need to concentrate on listening. When poor fit ear pads (cups) at the closed headphones worse bass response, so I closed headphones with a bow pressure produced by them on the head, usually higher than the open.
7. On resistance:
- Low resistance – resistance from a few ohms to a few hundred ohms;
- High resistance – resistance from a few ohms to a few tens of ohms.
Headphone icon. Placed to identify the connectors, controls, etc.
The main technical characteristics are: frequency range, sensitivity, resistance, maximum power and distortion as a percentage.
1. Frequency characteristic of audio output device
This behavior has an effect on the sound quality headphones. Headphones with a large diameter membranes have a high quality sound.The average value of the frequency response of 18 Hz - 20,000 Hz . Some professional headphones have a frequency range of 5 Hz to 60,000 Hz . The widest frequency range stated on some models up to 5 Hz - 125 to Hz .
2. Sensitivity of audio output device
Sensitivity effect on the volume of the headphones. Typically headphones provide the sensitivity of at least 100 dB at a lower sound sensitivity may be too quiet (especially when using headphones with the player or similar audio output devices). Affects the sensitivity of the magnetic core material used in headphones (e.g., neodymium magnetic cores). Earphones “ear” with a small diameter membranes have a thin magnet.
3. Resistance (impedance) of audio output device
It is important to match the full value of the modulus of the electric resistance of headphones and the output impedance of the source.Most headphones designed for resistance to 32 ohms . Headphones with an impedance of 16 ohms have increased radiated acoustic power.For studio use headphones with a maximum value of impedance.
4. Maximum capacity
Max (passport) power input determines the volume.
5. The level of distortion
The distortion level of the headphones audio output device is measured as a percentage. The smaller the percentage, the better the sound quality.Headphones distortion introduced by less than 1% in the band from 100 Hz to 2 kHz are suitable, whereas for bands below 100 Hz is acceptable 10%.
Types of connectors
- Jack ;
- Mini-Jack ;
- Micro-Jack .
2.2 Input audio information
For audio input devices information include microphones. These devices convert sound vibrations into electrical.
The microphone is used for sound input into a computer. Continuous electrical signal coming from the microphone is converted into a numerical sequence. This work is done by the device connected to the computer, which is called the Audio Adapter, or a sound card.Playback of recorded sound in the computer memory also comes with audio adapter that converts the digitized sound into an analog electrical audio signal input to the speakers or headphones. It follows that the sound card combines the functions of the DAC and ADC.Fig. 2 “Converting sound input and output” illustrates the described process.
Despite the fact that the speakers or headphones are not technically part of the MPC-specification are specifically necessary for sound reproduction. Furthermore, the voice input information used for sound or voice control computer requires a microphone. Systems equipped with sound cards usually also contain low-cost passive or active speakers, which can of course be replaced by a more suitable size speakers or headphones, which provide the required quality and frequency characteristics of the reproduced sound.
Multimedia computer with audio output devices such as speakers and a microphone, has a number of features:
- Adding stereo to entertainment (gaming) programs;
- Increasing the effectiveness of educational programs (for small children);
- Adding sound effects in the demonstration and training programs;
- The creation of music using the hardware and software MIDI;
- Add a sound file;
- Implementation of network audio conferencing;
- To add sound effects to the events of the operating system;
- The sound reproduction of the text;
- Plays audio CDs;
- Playback file format. Mp3;
- Playback of video clips;
- Plays DVD-movies;
- Support for voice control.
Thus, our present life is unthinkable without the computer, and now the computer (as well as established on the basis of consumer PCs and other equipment) we are no longer present today without the audio output device, including sound.