SHARC Melody platform incorporates automatic room tuner (ART) technology

Create the ideal surround sound for the mass market

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The advent of the digital audio era has revolutionized consumer audio and home theater systems. With the emergence of new situations, such as the rise of DVD, the birth of new multi-channel audio formats, and the widespread use of digital signal processors (DSPs) in audio systems, high-end surround sound audio is beginning to open to the general consumer. . As the sales performance of home audio systems is expected to continue to grow rapidly, manufacturers are making every effort to create differentiated products, adding new models of various models as soon as possible, consolidating market share and reducing system and development costs.

In the face of high market demand, Analog Devices has introduced the latest SHARC processor family in time to combine the SHARC® Melody® platform to implement Auto Room TunerTM (ARTTM) technology, simplifying the deployment of complex audio systems. At the same time, the listening experience is greatly enhanced. In general applications, the ART software resides in the surround sound receiver of the SHARC Melody platform. ART technology automatically measures and corrects the acoustic characteristics of a multi-channel sound system based on the specific conditions of the system's installed room, compensating for non-ideal room acoustics and speaker response.

The complete audio processing capabilities of the SHARC Melody platform converge on ADI's outstanding research and development in the professional audio field. The integration of ART technology gives manufacturers a new advantage in designing products that are close to the general public. Developers can now benefit from cost-effective, user-friendly technologies that create a thrilling surround sound experience for the average consumer that can only be enjoyed in concert halls and movie theaters.

Surround sound is becoming more and more popular

For many years, realistic surround sound has always been a “patent” for hi-fi enthusiasts, and the expensive installation of components and professional technicians has made the general crowd discouraged. As technology changes with each passing day, costs and prices continue to drop, and manufacturers finally have the opportunity to let more people enjoy the charm of surround sound and multi-channel audio.

The home theater system is one of the most popular results, especially the stand-alone home theater (HTiB) suite, which bundles a complete set of audio components (with the necessary interfaces). The HTiB system includes an AVR DVD player and six speakers, starting at about $300, so it's no surprise that surround sound is becoming more popular among DVD consumers.

As the general public also has the opportunity to experience a variety of moving sound effects, audio developers are faced with many new challenges while discovering new opportunities. For example, the settings of the surround sound system have been complicated, and even high-end audio systems are difficult to configure the best sound. Speakers are often placed in poor locations due to indoor space limitations. Users rarely calibrate the delay and gain of each speaker according to the general procedures documented in the manual. The bass management parameters may be incorrect but not modified; the speakers may be out of phase or simply not connected. Although loyal audio enthusiasts may hire technicians or are happy to solve these trivial problems, vendors are aware that unless surround sound installation becomes more user-friendly, it is difficult for general users to be satisfied.

Hardware specification requirements

Hardware Configuration

Target Processor: SHARC ADSP-21xxx
External memory

- Flash: 1MB (1M*8 bit wide)

- SRAM: 1MB (8-bit wide; 256K x 32-bit)

Oscillator microphone (provided by OEM)

Host interface

Serial Peripheral Interface (SPI)
Clock / Strobe / MISO / MOSI

Serial audio interface configuration

Automatically set sampling frequency range: 44.1 kHz or 48 kHz
Room equalizer sampling frequency range: 32 kHz–192 kHz (depending on the sampling frequency of the input signal)
Input port configuration: up to 10 channels output port configuration: up to 10 channels

ART concept

ADI's ART technology enables automatic equalization and calibration operations, and its efficiency and economy enable audio system vendors to meet challenges and seize opportunities. The ART concept takes full advantage of the DSPs commonly used in today's surround sound devices. These DSPs are becoming cheaper and more powerful, and the audio decoding algorithms they originally designed to implement have been standardized. Therefore, you can use built-in processing to improve sound quality.

A special advantage of incorporating ART software into the SHARC Melody platform in a surround sound system is that the room equalization function can be directly integrated with the receiver's other functions - performing equalization operations compared to expensive, complex external components. The early system has made significant progress. So the ART solution minimizes the cost of adding sound-optimized components; just add the ART software and the microphone to get the job done. Another outstanding advantage is that the SHARC processor provides 32-bit floating-point DSP performance to make system cost competitive, ensuring high performance and cost-effectiveness of the entire on-chip audio processing function.

Moreover, the ART technology based on the SHARC Melody platform complies with the trend of using subwoofers and small satellite speakers in the HTiB package. The sound quality of low-cost satellite speakers can be greatly enhanced by the corresponding room equalization function, which helps audio system developers to bring a satisfying listening experience to consumers at a lower cost.

Factors affecting sound quality

Why is it so difficult to achieve the best room balance? The reason is that there are various factors and changes in the actual listening environment that will work. Ultimately, the effect of sound playback depends primarily on the quality of the speakers, the acoustic properties of the listening space, and the placement of the speakers relative to the listener.

High-quality speakers reproduce sound over a wide frequency range, and front-end radiated power rarely changes with frequency. Low-quality speakers tend to have an inhomogeneous frequency response that attenuates certain frequency ranges while attenuating other frequency ranges.

Another important attribute of a horn is directionality, which varies with frequency. The directionality of the horn depends on the size and shape of the cabinet and the properties of the transducer used. The horn tends to radiate very high frequency sound only in the direction indicated by the speaker, and radiates very low frequency sound in all other directions. Therefore, the horn frequency response measured under the muffling (no echo) condition varies greatly with the measurement angle.

Since the sound is reflective on various surfaces of the room, the frequency response of the listening space becomes very complicated. The resulting reverb has a time-responsive characteristic: first a small number of significant reflected waves, followed by a dense reflection in each direction, the latter commonly referred to as delayed, diffuse reverberation. At the low frequencies corresponding to the room vibration mode, the frequency response of the room contains significant peaks; in the case of a given room size, the frequency of the peaks can be calculated directly. At higher frequencies, the mode density becomes so high that the frequency response is statistically significant and has the characteristics of closely spaced peaks and troughs.

The overall waveform of the frequency response depends on the absorption characteristics of the room material; because the porous material is more absorbent at high frequencies, the higher the frequency, the less the amplitude of the room response. In addition to low frequency or early stage, it is best to describe the room response by statistical methods. As the measurement point moves within the room, the precise details of the response will change more difficultly, but the overall envelope of the response will not change much.

The speakers are preferably placed equidistant from the listener, depending on the playback format. The ideal stereo system is placed at an angle of +/- 30 degrees to the listener. In a 5.1 channel surround sound system, the center speaker should be placed directly in front of the listener, and the surround speakers should be placed 110 degrees on both sides. The placement of the subwoofer is not very important. In most listening environments, it is difficult to place the speaker in the ideal position of the listener, resulting in an unbalanced sound image. If the listener is closer to one of the speakers, the closer speaker will dominate the sound image because its sound arrives earlier and louder. In addition, the surround sound system may be equipped with speakers from different manufacturers and the acoustic characteristics may not match exactly.

As a well-designed room equalization system, ART software attempts to compensate for all of the following factors: frequency response and directionality of each speaker, room frequency response, positional relationship of the speaker relative to the listener, and improper installation.

Design features: humanization and functional integration

ART technology based on the SHARC Melody platform is designed for the consumer market. The software has been built into a fully automated system that allows inexperienced users to achieve satisfactory results quickly and easily in their own rooms. Some consumers are no strangers to technology, but they are worried that the more functions they have, the more complicated they are. They don't have enough time or money to install them effectively, so they are not willing to choose surround sound, and the advent of this new technology is completely eliminated. The concerns of these consumers.

Although designed for affordable applications, the ART software is still comparable to the best high-end room equalizers on the market. The ART algorithm is a high quality implementation based on state-of-the-art signal processing and pattern recognition technology. The mass market values ​​both the latest features and the ease of operation. Therefore, with the ART software, manufacturers can not only bring excellent surround sound systems to the market, but also gain differentiated advantages for themselves.

ART technology is designed to meet the following requirements:

Automated, robust, fool-proof, one-time quick measurement; just one point of measurement, the main listening position without the need to predict the speaker, room and other parameters; all audio system information is automatically determined for the full range of SHARC Melody platform Improve the sound quality of the room, covering a larger range of optimal listening, so that many listeners can experience excellent sound quality

First-class surround sound optimization - fully automatic

The use of ART technology to measure and correct the response of a multi-channel audio system shows unusual human characteristics. The user first installs the receiver and speaker and places the microphone in the main listening position. (The receiver OEM provides a microphone, which may be built into the remote control to avoid single-connecting the microphone on the receiver.) The user then starts the calibration and equalization process via the receiver's remote control.

The ART software emits noise at each speaker to measure the sound system. During the calibration process, the user can hear a pink noise measurement signal that is milder than white noise and more pleasing than the hum, hum and squeak used in other systems. Each utterance lasts for 1.5 seconds, followed by a few seconds of silence. The microphone at the listener's location records the noise, and the SHARC processor located in the receiver analyzes the acquired signals.

The ART algorithm works with the SHARC processor to calculate a large amount of information related to the user's sound system, such as the sound pressure level (SPL) of each speaker, the distance from each speaker to the listener, and the frequency response of each speaker. This information is primarily used to apply gain, delay, and pitch correction during sound playback to improve sound quality. The ART software also automatically configures bass management parameters. The ART algorithm corrects for defects in the entire audio system after actual installation, such as speaker response and directionality, room reflections and reverberation, unsatisfactory speaker and listening position, and improper installation.

Except for a series of startup operations, the user does not have to know any complicated procedures in the process, except of course the user is interested to know. You can do everything with a one-time quick measurement at the main listening position. In just a few minutes, the ART software and the SHARC processor can measure, calculate, and compensate for the actual acoustic characteristics of the installed equipment (manual operation takes longer). Therefore, the sound quality of the main listening position and even the corners of the room has been greatly improved. Users can experience this change: as long as the equalization function is enabled and disabled during playback, you can immediately feel the sound quality.

Because of the speed, simplicity, and superior performance of this new technology, it is highly appreciated by users, helping them recalibrate the system after changing room layouts (such as moving furniture locations) or repositioning surround sound devices.

Automatic parameter setting

After completing the one-time measurement of each of the above audio channels, the ART Auto Setup function automatically detects the following parameters:

Whether the speaker is present. Did the user forget to connect a speaker?
Reverse polarity. Is the speaker out of phase wiring?
Speaker sound pressure level (SPL), unit dBC. This information is also the information indicated by the C-weighted sound level meter, which can be used to measure the perceived loudness of the speaker level.
Distance to the listener (delay time: milliseconds). This parameter is used to set the compensation delay for each speaker. When the ART function is not yet available, it is common practice to measure the distance with a tape measure.
Identify the speaker type. Is it a subwoofer? Is it a large or small satellite speaker? The latter is essential for bass management configuration. The speaker is considered to be a large satellite speaker when reproducing frequencies below 80 Hz.
Determine the roll-off frequency of each main and subwoofer in Hz. This is another parameter needed for proper bass management.

Comparison of ART technology before and after application

The ideal speaker exhibits a perfect "flat" shape in the frequency response in an anechoic environment. Under ideal room acoustic characteristics, the frequency response should be flat until 2 kHz and then roll-off at -1.5 dB/octave at higher frequencies. The dashed line represents the target curve, showing this ideal response. ART adjusts the speaker response to better match the ideal speaker response in an ideal listening room.

It also shows that ART adjusts the total gain of the speaker. In the pre-correction diagram, the gain is too high (ie, the speaker is too loud). In the corrected graph, the gain has been reduced to the desired target level.

Before correction

After correction

Automatic equalization and compensation

The ART algorithm and the SHARC processor calculate coefficients based on the parameters and data generated when analyzing the "automatic settings" and then use the coefficients to perform automatic equalization and compensation. Related adjustments include:

Compensates for the delay of each speaker in milliseconds. The sound of different speakers will reach the ears of the listener at the same time. If you don't compensate for the delay, the listener often feels that the sound comes from the nearest speaker.
Compensate the gain of each speaker in dB. Compensating for the gain of each speaker is critical to restoring the correct volume balance between the speakers.
Compensate for the equalization parameters of the speaker. This adjustment includes pitch equalization to compensate for non-ideal speaker and room response. The equalization operation is performed by the parametric equalizer. The parameters for each band are as follows: center frequency, gain, and bandwidth (Q). The number of bands per channel is set by the receiver OEM.
The graphic shows the equalization curve for the user to edit. Graphic display and editing allow audiophiles to adjust to their own requirements. This feature is implemented because the ART uses a parametric equalization filter. In addition, the receiver manufacturer can allow the user to perform manual equalization operations based on custom coefficients as needed.

Flexible customization, faster time to market

The development of ART technology is based on meeting the needs of mass-market consumer audio, so ADI has equipped the software with a variety of design and development features. Surround receiver designers can develop custom features while reducing development risk and cost and time to market, enabling the development of models with different features and price points.

The flexible and customizable features of ART software include:

Support for any speaker configuration. ART supports any number of channels (ports). It automatically detects the channel and the connection status of each channel and subwoofer or speaker. This feature is not only user-friendly, but also allows manufacturers to more flexibly package the system, including different numbers and types of speakers.

Support microphones provided by OEM manufacturers. The ART software compensates for non-flat frequency response curves (the flatter the curve, the better the measurement), allowing measurements to be made with inexpensive microphones. The system designer can specify the frequency response of the selected microphone.

The user interface is customizable. In general, the receiver can demonstrate the measured channel and related information of the channel through the video screen. Receiver OEMs can easily modify the ART interface to increase consumer usability and product differentiation.

Users can customize the target equalization effect, each with unique sound effects that can be preset for specific market segments. Users can choose settings such as "classical" or "rock".

The next-generation SHARC processor integrates all the necessary audio functions (including the ART algorithm) into the chipset, minimizing development risks and costs and speeding time-to-market. The SHARC processor not only has industry-leading floating-point performance, but also features at least twice the performance of a single MAC (multiply-accumulate) fixed-point device. In addition, SHARC processors support the latest audio decoders and post processors such as Dolby® ProLogic® IIx and Microsoft® Windows Media® 9 Audio Professional, with enough on-chip memory to support studio-grade audio processing. .

Moreover, the processor's programmable features make design upgrades (adding functionality, compatibility with new standards) more flexible. With the SHARC processor family, developers don't have to use peripherals or software plug-ins to implement functionality. Nowadays, manufacturers are providing an increasingly rich audio experience for ordinary consumers. Manufacturers must obtain the ideal price and fast turnaround time to profit from it. Therefore, the SHARC processor integration solution can not only meet the needs of manufacturers, but also they cannot. Short.

All SHARC processors are fully supported by Analog Devices' VisualDSP++TM integrated development environment, which includes a complete set of software tools, a highly optimized C++ compiler and a graphical development environment.
ART and SHARC Melody Platforms – Keeping pace with the consumer audio market

Based on ADI's robust SHARC Melody platform, ART technology helps audio system developers create rich multi-channel audio that is appealing to home audio receiver consumers and benefit from emerging market opportunities. ART software and the SHARC Melody platform are not only affordable, close to the mass market, but also simplify the setup of home theater systems and compensate for non-ideal acoustic environments and speaker response, transforming the otherwise complex process into a highly humanized listening experience. .

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