Components of the audio systems

            Hi-FI audio acquisition and recording systems

High fidelity audio acquisition and recording is done with professional equipment of a certain class (and cost), the first link in the chain which is also the most important is the microphone.

The microphone is a transducer in charge of converting sound waves into electrical voltage variations, there are piezo-electric, condenser, ribbon microphones  and carbon microphones, they are named according to the type of material used for the transduction. It is the most important component of an audio recording system, because it must convert sounds into electronic signals without creating distortions and in the most faithful way possible. They convert the sound waves of musical instruments and vocals into a very weak electrical signal that will be pre-amplified by an internal low-noise amplifier and then conveyed via shielded cables headed with XLR connectors (balanced connectors) to the input of the Mixer (or mixer).

 The mixer is an electronic device that takes care of receiving all the audio signals coming from the various microphones and from the pickups of the string instruments (cordophones) at its inputs, it is used to adjust the volume, the tones, the equalization and the amplification , and finally to mix them together simultaneously using potentiometers, at the mixer output we find the signals of the various musical instruments mixed together and ready to be recorded in analogue or digital mode. The mixer must have a sufficient number of inputs to allow you to connect the audio sources that we want to be part of the musical performance to be recorded and must have low noise, low distortion and high reliability, the inputs are numbered and the number of the input corresponds to that of the corresponding volume adjustment potentiometer, so that it is easy to identify the source to be adjusted. The mixer can be analog or digital, in this case the inputs can be directly digital and if you need to process analog signals, first convert them to digital using the A / D converters or the mixer itself can convert them via analog inputs and internal converters.

The A.S.P. (analog signal processor) or the D.S.P. (digital signal processor) are devices that process the audio signal in order to expand-compress its dynamics, add-remove spatiality and vary the volume and tones according to the timbre we want to associate with the musical performance to be recorded.

The recorder is the device that fixes the signals coming from the mixer and the ASP-DSP on a reproducible medium and therefore makes the musical performance or speech permanent. Once upon a time, recordings were made in analog on magnetic tape with a low-noise reel-to-reel recorder and a minimum scrolling speed of 19.2 cm/S, in order to have excellent audio quality. With the advent of digital, recordings are made directly in digital via a workstation in Wav format (without compression) with a most large sampling frequency, this guarantees a very high frequency response and almost no noise. Digital audio files can also be acquired via a D.A.T. (digital audio tape) recorder.

With the recorder at the end of the recording chain, the MASTER copy or mother copy is obtained, that is, the first original copy of the performance, from which the mother recording of the vinyl records and the master compact disc after equalization, will then be obtained.

In the performances that are to be recorded in live environment and not in a recording studio, all the equipment described above is usually housed in a container or van placed near the stage where the performance takes place, the recording is then taken to the studio for further processing.

Below are some enlargeable figures that will help you better understand what has been explained.

 Schematic of a record-quality recording system

 Professional microphone with anti-pop protection

   Shielded cable with XLR connectors

                                         Reel tape recorder                          

                                   Professional Digital D.S.P.   

                             Audio production and mixing studio

                                     Professional audio Mixer

                        Legendary LA-2A Analog Optical Limiter

Master recording on analog tape (1980), vinyl records and compact discs will be recorded from the master tape after equalization

                      Hi-Fi Audio Playback Systems

Audio reproduction can be done with both high quality (and high cost) equipment and with less expensive (but less performing) systems, in any case the reproduction chain remains the same, the difference will be appreciated when listening which in the case of low cost equipment will be less satisfying and less defined. It must be kept in mind that to obtain high fidelity audio the entire chain must be made up of Hi-Fi equipment of the same class, even the audio support to be reproduced must be, otherwise the audio quality drops significantly.

Below is a block diagram of a Hi-Fi audio playback chain.

Let's start analyzing the equipment in the chain:

The turntable is a device used to reproduce audio recorded on vinyl records (or sealing wax in the past) on both sides. It consists of an electronically controlled electric motor that rotates an aluminum platter at a constant speed. The record to be played is placed on the platter. A head equipped with a diamond stylus slides between the grooves of the record and transduces the ondulations of the same grooves into sounds, the signal obtained from the head is amplified and sent to the input of the preamplifier equalized according to the R.I.A.A. regulations. At the end of one side, the record must be turned over and the stylus must be repositioned on the guide groove to listen to the other side.

Records can be supplied in various standardized formats and at different playing speeds. The standard formats are 16 rpm (past tense), 33 rpm (long playing), 45 rpm (contained only two performances) and 78 rpm (in the past). Obviously, before starting to play, you need to set the right rotation speed on the turntable.

The vinyl record disc was widely used in the past, then with the advent of digital it was progressively abandoned, in the current era it is slowly coming back into fashion together with thermionic tube amplifiers simply because it is able to return a sound timbre unmatched by digital, very warm and rich in detail.

                                      Disc with grooves highlighted

                                    Head on a microgroove disc

The tape recorder-player reproduces the sound previously recorded on a magnetic tape medium (reel or compact cassette), the tape moved at a constant speed by a dedicated mechanism while it slides from one reel to another passes in front of an air gap obtained on a permalloy head inside which is housed an electric coil, which by the principle of self-induction transduces the orientation of the magnetic particles deposited on the tape (pre-oriented by the recorder) into a weak electrical signal, at this point via the selector the audio signal is sent to the audio power amplifier to drive the loudspeakers. 

The recording process on tape occurs in a completely reverse way from what was said above, the input signal is amplified-equalized and sent to the recording head which transduces the electrical signal into orientation of the magnetic particles on the tape (magnetization). Before being recorded, the tape must be prepared (premagnetization), that is, the particles must be pre-oriented in a chaotic way (BIAS current), this is true whether it is a new magnetic tape or whether you are using a tape that has already been recorded (erasure), a dedicated head takes care of this which is located before the recording-playback head, to which the BIAS current is applied. What is important is that the air gap of the recording-playback head is correctly oriented with respect to the moving tape (azimuth), otherwise the reproduction will be poor on other players with well-aligned heads, the alignment is carried out via a spring and a screw on the head and by reproducing a test tape recorded according to the correct standard.

                                      Magnetic tape reel       

            Tape deck mechanic for compact-cassette

The multiband tuner is a superheterodyne radio receiver built according to the dictates that you can find on the Radiowave page of this site in the Receivers section. It is capable of receiving the medium wave band in A.M. and especially the VHF II and III band where FM (analog) and D.A.B.+ (digital) transmissions occur, which allow for Hi-Fi reception quality. With the multiband tuner you can receive commercial broadcasts, which provide a vast repertoire of music and news.

The multiband tuner must be very carefully designed circuitry, this is because it must have impeccable frequency stability, very high sensitivity to weak signals, a very respectable signal-to-noise ratio and must provide Hi-Fi audio quality, it can have analog tuning with a cord and variable capacitor with a talking dial display, or electronic tuning with varicap diodes with a 7-segment digital display.

               Multiband tuner with varicap diode digital tuning

The Compact Disc (C.D.) player is a digital electronic device made up of precision mechanics and an electronic circuit designed to convert audio from digital to analog D/A. It can however have a digital output without conversion if the subsequent preamplifier-selector is able to process this type of signal.

The CD is made up of two transparent plastic discs glued one on top of the other, between the two discs is  trapped a membrane sensitive to laser beams having a pre-established wavelength, during recording the LASER beam strikes (burns) the membrane of the sectors (non-reflecting signal 0) and leaves others free (reflecting signal 1) in order to digitally record the musical information.

During playback the player, through a LASER pickup of the correct wavelength (precision and complex component), reads the non-reflecting sectors (0) and the reflective ones (1), thus reconstructing the digital signal previously recorded on the CD. A high quality A/D converter takes care of transforming the digital information into a high fidelity analogue one and transfers it to the shielded output sockets. The procedure just described is a very complex process, made possible thanks to the high quality  mechanics and  and high precision optical components, microelectronics has then transformed the complex control circuits of the mechanical-optical components and signal conversion into others that are easier to manage and produce, without the technology of integrated circuits the costs would have been prohibitive and probably the digital audio revolution would never have happened. It should be noted that the CD has allowed for very high quality audio free from background noise and scratches, this is because reading occurs via a laser beam and therefore without physical contact between the pickup and the audio support.

                               CD player with LASER pickup        

                             Analog and digital audio media

In the last few years, the USB (universal serial bus) digital port has also appeared on audio systems, which allows you to connect so-called USB sticks containing FLASH-ROM memories that can be used to store audio files in compressed MP3 (MPEG layer3), WMA (Windows media audio) format or other supported formats. A special integrated electronic circuit reads and decodes the compressed files, converting them to analogue and restoring, as far as possible, the original audio quality damaged by compression.

The preamplifier selector is a very important piece of equipment, it accepts at its inputs the signals coming from the various audio peripherals seen before and through a switch it allows you to select them one at a time, sends the audio signal to be recorded to the recorder (tape, USB or CD burner), modifies its physiological characteristics through the tone controls or DSP-ASP, regulates the output level (volume) and finally amplifies it in voltage to the right level so as to drive the subsequent low-frequency power audio amplifier.

The preamplifier must be low noise, must amplify in voltage and have very low harmonic distortion, the selection switch (mechanical or currently of the electronic switch type) must be of excellent quality and extremely reliable. The preamplifier-selector can be either analog or digital, the inputs and circuitry change between the two types, in the case of digital a certain number of A/D converters must be foreseen to allow it to work with analog audio peripherals. This equipment can also be found in combination with the power amplifier, in which case it is called an integrated amplifier.

                 Block diagram of an integrated amplifier

 The audio power amplifier receives at its input the conditioned and pre-amplified signal previously from the preamplifier selector and amplifies it in power (current and voltage) according to the needs of the listening environment or the user's preferences, it is a complex device, and must be designed without compromises, because it must not add distortion and noise to the amplified signal.
There are power amplifiers of various types and operating classes, the cost is directly proportional to the quality of the components used and the power to be obtained, the amplifier will then have to drive the speakers, which have a complex operation and that is not purely resistive but sometimes inductive or capacitive, so it must have a good capacity to deliver power without having difficulty with particular loads or when a surplus is required.
Recently, digital amplifiers in D class have appeared on the Hi-Fi market, they work through P.W.M. technology (Power width modulation) and allow to obtain high power with little heating (high efficiency), traditional amplifiers instead work in class A or A-B and do not have a high efficiency, but in the case of class A they provide an impeccable audio quality.

Below are some simplified schematic diagrams:

Simplified diagram of a push-pull power amplifier

                          preamplifier with tone control

Loudspeakers are devices usually built with wooden panels and contain the speakers inside, that is, the transducers responsible for transforming the electrical signal coming from the amplifier into sound pressure and trying to do it in the most faithful way possible.

The speakers for HI-FI are made up of a copper coil, which is integral with a paper or polypropylene (or aluminum) membrane, the membrane is supported by a corrugated canvas damper and the whole thing is mounted on a metal basket via a rubber or foam suspension. The coil is immersed in the air gap of a powerful permanent magnet and by applying the signal coming from the amplifier to it, the coil moves in the air gap and transduces the audio signal into sound waves. The speakers are divided into three types, the Woofer, that is the speakers with a membrane, coil and large magnet to reproduce the low frequencies (low resonance frequency), the Midrange for the medium frequencies, which have a smaller magnet and membrane and finally the Tweeter which are used to reproduce the higher frequencies and have small membranes.
The loudspeakers with three speakers inside (three-way) are able to reproduce all the audio frequencies very well (from 20Hz to 20000 Hz) thanks to the speakers optimized for each frequency, the speakers must be driven with the right frequency band to avoid damaging them so their input must be preceded by a Cross-over filter, that is a system of passive filters that includes a low-pass filter for the Woofer, a band-pass filter for the midrange and a high-pass filter for the tweeter. Cross-over filters must be of good quality and with constant impedance to avoid excessive power losses and damage to the power amplifier, furthermore they must be well calculated from the point of view of the cut-off frequencies to prevent damaging the speakers by sending signals with frequencies that are difficult to manage.

The speaker box must be well closed and with sound-absorbing material applied to the internal walls to block the rear radiation of the speakers which, being in antiphase with the front one, would cause an attenuation of the sound pressure especially on the low frequencies. There are also two-way speakers, with only Woofer and Tweeter, they provide a fairly good fidelity but not equal to the three-way ones.

                            Wiring diagram of a three-way speaker 

                                      Woofer Loudspeaker

                                           Vintage three-way speaker  

                                           Two way speaker

                     Vintage HI-FI system with separate components

         Compact and multifunction quality hi-fi

I repeat that it is impossible to condense in this small text the immense world that is behind the phrase "Electronics and Audio" but if you need clarification or advice you can write to me at the address shown on the "Contacts" page

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