The internal arrangement of a digital audioplayer

Evgenie Rudometov

rudometov@rudometov.com

Recently the wide circulation was received by compact, transportable, digital audioplayers. A basis of the given arrangements are modern semiconducting units, including specialised processors of processing of an audiocontent

Thanks to successes of solid-state technologies permanently there are new arrangements. Many widely known electronic products promptly "grow thin", decreasing in the sizes. That of it to be convinced, it is enough to recollect computers.

There is no time the enormous and accident-sensitive computing "monsters" occupying hundreds of square metres and "devouring" hundreds watt of the electric power, today in the refreshed variants rather simply find room on desktops. Moreover, the compact pocket computers which are easily located on a palm, on computational capability many times over exceed powerful computing systems of a first generation. Well and to compare the first computers to the notebooks possessing a wide band of functionality, in general it is incorrect.

Considering evolution of solid-state technologies, it is necessary to mark, that miniaturization processes have mentioned not only the big and small computers. The given process has captured also home electronic arrangements which number video and an audio equipment concern. Stationary systems became more compact, and transportable not only have decreased in the sizes, but also have found new functionality.

The place in full or in part analogue transportable instruments was occupied with the miniature digital devices capable autonomously to handle video and an audiocontent. And if portable videosystems to some extent are exotic – their time, as a matter of fact, has not occurred yet audioplayers have already strongly captured the consumer market. These compact, easy digital audioarrangements are presented now in tens, and can be even in hundreds models. Their release is calculated already in millions pieces and continues to increase fast with a gain in tens percent a year. High rate is saved within several years.

It is necessary to mark, that not in the last instance prompt growth of popularity of these arrangements was promoted by release of new electronic units, perfection of the architecture of arrangements, improvement of interfaces and the algorithms of coding supported by the system and applied software. By the way, despite a resistance of the corporations which are engaged in duplicating and implementations of sound writings, various algorithms of compression of an audiocontent have found the wide circulation. Moreover, MP3 and WMA became, as a matter of fact, branch standards and have found the incarnation in numerous digital devices. As the recognition of this fact, digital audioplayers have received the name «MP3 players».

This name became conventional in spite of the fact that the given arrangements, as a rule, not only support some formats, but also quite often possess functions of writing from a microphone, that is are dictophones. Besides, the majority of them is provided with writing and audioinformation coding through a linear analogue input terminal. In addition to it many of the given arrangements are supplied built in FM by a radio receiver. And, of course, all players have the digital input terminal intended for "downloading" of an audiocontent numerically from the personal computer or a notebook. Recently for this purpose use ports USB 2.0 providing a transfer rate to 480 Mbit/with.

All these possibilities are supported by an appropriate electronic stuffing of digital players. Despite an abundance of used active and passive radioelements, an architecture basis is the limited quantity of chips. Among them the central place occupies the audioprocessor providing processing of an audiostream, including compression and decoding of data, and also handle of other components of a player.

The simplified circuit of the architecture of a typical digital audioplayer is resulted in a Fig. 1.

Fig. 1. The circuit of operation of digital audioplayers

It is necessary to mark, that the structure of all players includes the nonvolatile memory which is for operation and durable, practically non-limiting, to storage time of the audioinformation even after electrical obestochivanija of the electronic circuit of a player. Non-volatility also consists in it. As such memory now in the architecture of audioarrangements hard disk drives and flash-memory chips use. The first of them are characterised by high size and low cost of an information storage. However it is reached at the expense of the raised power consumption on matching of competing solutions, and also bolshego size and weight. The second provide the big compactness of systems at their rather high energoekonomichnosti.

Changeover in portable audiosystems of analogue media, before presented basically the magnetic tapes, has introduced appropriate corrective amendments in used components and the architecture. Despite an abundance shemotehnicheskih solutions, main principles remain invariable. They also consist, first of all, in conversion of the analogue signals carrying the information on a sound, to a digital code.

This operation is carried out by the so-called analogue-to-digital converter — the analogue-digital converter. The principle of its operation consists in measurement of levels of power of an input signal at regular intervals with rather big frequency. This frequency corresponds a minimum to the doubled frequency of the upper component of a frequency spectrum of an audiosignal. It means, that if the upper frequency of a player makes 20 kgts frequency from which measurement is carried out, should be a minimum 40 kgts.

The gauged values of the analogue-digital converter will be converted to by a multidigit binary, digital code. From number of used bits — the band of a binary representation of a useful signal depends on the smallest to the greatest possible values. Accordingly all gauged levels of an audiosignal correspond to the digital values allocated in a band of binary numbers from all nulls to all units. It is necessary to mark, that at 16 bits making 2 bytes as for traditional audio of CD, the possible band makes more than 90 db.

High rate of removal of countings and performance of conversions guarantees a wide frequency range, and shestnadtsatirazrjadnoe coding — the big dynamic range. However all it generates files of the considerable size, appropriate sizes of the built in nonvolatile memory demanding for the storage. So, for example, 60 minutes of quality of CD are about 600 Mb. For memory size saving use coding with usage of various algorithms of compression. The wide circulation was received by algorithms MP3, and also WMA.

Providing comprehensible lowering of quality of the audiosignal, the specified algorithms of compression essentially reduce the sizes of files. So, for example, compression MP3 to value of the data flow in 128 Kbit/with (the most widespread level of compression for the musical information) reduces the audiofile size in 10 times. And stream usage in 256 Kbit/with provides file size abbreviation approximately five times. Thus the quality provided 128 Kbit/with MP3 as consider, perhaps, the majority of users, it is quite enough at usage of miniature headphones.

Conversion of the initial digital signal for which source the audio of CD is, for example, is carried out or by means of the desktop personal computer, or a notebook with subsequent "zakachivaniem" the transformed file by means of become standard ports USB in a digital audioplayer. Well and, of course, the majority of advanced models give possibility of conversion of the analogue signal arriving from a linear input terminal or a microphone, resources of the audioplayer. The built in analogue-digital converter for this purpose uses, and conversion on algorithms MP3 is carried out by the player audioprocessor.

The handled signal is written in the nonvolatile memory, whence in a total playing time of the audioinformation it is exposed to reconversion from the compressed state in the usual not compressed digital code. This operation is carried out also by the audioprocessor.

Well and from not compressed digital code back in an analogue signal conversion fulfils an appropriate unit — the digital-to-analogue converter — the DAC which have been built in also in electronic "stuffing" of an audioplayer.

Further strengthening of an analogue signal osushchestvljut special electronic circuits. They can be fulfilled or in integral sort on the basis of chips, or by means of digital units on the basis of transistors, usually field.

As to type of the built in nonvolatile memory taking into account fast growth of size and reduction of price of appropriate chips of so-called solid-state memory the direction of the digital audioplayers created on the basis of the flash-memory fast develops.

Really, for example, the number of the models created on the basis of this type of memory, permanently increases. By the way, numerous press releases of company Creative testify to it — one of leaders of audiosolutions. Now on a firm site 9 models are presented. With the registration of press releases of such models much more.

As an example of compact, desksize digital audioplayers characterised in small weight and the big functionality, it is possible to result model Creative Rhomba NX.

The digital audio player Creative Rhomba NX is the compact audioarrangement, differing ergonomic design. It conveniently is located in a hand and is controlled by means of miniature keys and the built in graphics display. It is supplied by functions of operation with FM radio. Provides playback and writing. This player possesses memory of 256 Mb and supports interface USB 2.0 that allows to load musical files from the PC with a speed about a song in a second. It is capable to memorise to 60 songs in format MP3 or 120 songs in format WMA (at average duration of a song of 4 minutes - 64 Kbit/sek WMA, 128 Kbit/sek MP3). The player eats from two standard batteries AAA which continuous playback suffices at 14 o'clock. Concerning big ZHK the screen with blue highlighting provides evident and fast access to all functions. Player Creative Rhomba NX allows to carry out writing with simultaneous conversion in MP3 any linear entering signal, and also with FM radio and a microphone.

Package of delivery of audioplayer CreativeRhomba NX

Photo 1. A package of digital audioplayer Creative Rhomba NX

Key parametres of audioplayer Creative Rhomba NX

Photo 3. Appearance of digital audioplayer CreativeRhomba NX

The minimum system requirements

Basis of an audioplayer of audioplayer Creative Rhomba NX is audioprocessor Philips SAA7750EL chip. The fragment of the printed circuit card of a player with this processor is resulted in a Fig. 3. Controller USB of 2.0 Phison corporations  — PS2002 is here too presented , ЖК plugs of the display, a linear input terminal, headphones, multifunctional navigation buttons (in the disassembled sort), the locking switch (hold) navigation buttons, spring contacts of batteries, others active and are passive electronic units.

Fig. 4. A fragment of the printed circuit card of audioplayer CreativeRhomba NX

Processor Philips SAA7750EL structure includes a kernel of the processor of processing of the audioinformation (kernel DSP) and 32 bits kernel ARM RISC. Here it is necessary to mark, that mentioned kernel ARM RISC is related, as well as all variants ARM RISC, to processors of the known set of Intel XScale which widely use in modern handheld computers and support ARM corporation command system. This system actually became the standard of branch providing high level of compatibility of a wide spectrum of arrangements, and also system and applied ON.

Presence of the specified features testifies to architectural perfection of the processor used in a player and its functionality, including computing power. It is necessary to add, that into processor Philips SAA7750EL structure enter also mentioned above the analogue-digital converter and the DAC. Integration of these components in structure of a chip of the processor allows to reduce number of chips.

Interface USB 2.0 is provided with chip Phison PS2002. The necessary information is displayed on built in a construction of player ZHK the display. Handle is carried out by means of touch keys and switches. Tuner FM radio is realised by means of chip Philips TEA5767 allocated on the special card, calculated for this chip with environing units of support. The sizes of this card slightly exceeds the sizes of the chip. This card is simply soldered to the main printed circuit card.

In a Fig. 4 the simplified architecture of audioplayer Creative Rhomba NX is resulted. On it the informational streams showing interaction of components a part the given arrangement are presented. Here it is possible to see basic elements of the architecture of audioplayer Creative Rhomba NX.

Fig. 4. The simplified architecture of audioplayer CreativeRhomba NX

It is necessary to mark, that the resulted architecture illustrating operation of audioplayer Creative Rhomba NX, it is possible to consider as typical solution.

In summary it is necessary to mark, as other known companies are not gathered to stand aside. Wishing to win the share of the market audiousrojstv, they release a considerable quantity of models. As a result on the given segment of the market the hard competitive struggle which result are fast perfection of this class of products at general lowering of their price was developed. All it raises popularity of audioplayers and promotes increase in number of users.

As to possibilities and the architecture of products of other manufacturers it is a subject already other articles.

Audioplayer CreativeRhomba NX is given by company EASTSIDE Consulting