SilentSeek
keyword Acoustic Noise, SilentSeek, Sinusoidal Seek, AAM
Since the invention of the Hard Disk Drive (HDD), seek time has been a general yardstick for drive performance. The faster the head is positioned over the desired track, the better the performance is perceived to be. These perceptions have driven the race for faster and faster seek times, historically to the sacrifice of acoustic noise quality.
However, in recent years, as personal computers are becoming more prevalent in the home and HDDs are being used for audio/video and entertainment applications, acoustic noise emissions are becoming important to consumers. In response to this new requirement, a number of new technologies have been developed to reduce the overall acoustic noise emitted by a HDD. The majority of the new technologies now being implemented are to suppress acoustic noise emission. One example is SAMSUNG's NoiseGuardTMtechnology (see the SAMSUNG NoiseGuardTMÂ Technology White Paper).
However, in pursuit of the ultimate reduction of HDD acoustic noise emission, SAMSUNG has developed another unique design called SilentSeekTM technology. SilentSeekTMÂ technology differs from NoiseGuardTMÂ in that it is designed to minimize the acoustic noise generated by the actuator movement, rather than suppressing the emitted acoustic noise.
During the past 10 years, outstanding developments in areal density increase and data processing speed have been achieved in HDD design to support the requirements of computation, which has been the main application of the HDD. In the past customers have chosen HDD products based on capacity, price and reliability. However, recently, as the application of HDD becomes more diversified, acoustic noise emission has emerged as one of the most important HDD characteristic. The reasons for this trend are:
- Personal computer end-users have become increasingly aware and critical of the acoustic noise generated by HDD. Low acoustic noise emission has become a perceived indicator of high quality. The average acoustic noise (in sound power level) of personal computer HDDs during normal read/write operation ranges from 3.0 bels to 4.0 bels. Considering that the typical environmental acoustic noise level at home, or in the office is about 4~5 bels, such a level of noise emission from a computer can cause concern, or even discomfort.
- New personal computer applications require quieter operation The proliferation of the Internet has brought the personal computer much closer to everyday life, and made it almost a necessity in the home. At home, the personal computer tends to be used more for entertainment with streaming audio/video. Excessive acoustic noise in these applications can be disturbing.
- Recently, affordable prices for HDD, coupled with very high capacity, have opened new opportunities for mass storage. High capacity HDDs can be used as the storage medium for digital content in consumer devices such as television, set-top-boxes, and digital video recorders. Movies, MP3 music, computer games and broadcast television contents are commonly downloaded, stored and replayed to/from the HDD. Since these HDDs will contain consumer Audio/Video content, excessive acoustic noise (especially noise caused by seeking) during content recording/playback may be unacceptable to the consumer. Also, since many personal computers may be located in bedrooms, the acoustic noise while downloading at night can disturb a good night's sleep.
Acoustic noise in an HDD can be classified into two distinctive categories, idle acoustic noise and seek acoustic noise.
Idle acoustic noise is defined as the sound level when the HDD is only spinning the recording media and has positioned the actuator over a specific track. Idle noise is generated mainly by the excitation from the ball bearings inside the spindle motor, and by airflow disturbances inside the HDD during disk rotation.
Seek acoustic noise is defined as the sound level when the HDD is dynamically moving and positioning the actuator assembly from one track location to another. During positioning, high frequency magneto-electric interactions along with the vibrations to the mechanical structure contributes additional acoustic noise (typically in the form of random "chirping" or "clicking" sounds) to the idle acoustic noise described previously. Influenced by the pursuit of higher performance, the seek operation has typically been designed to relocate the actuator as fast as possible. The best way in minimizing seek time is to maximize both the acceleration to reach a maximum velocity and the deceleration to return to zero velocity at the target location. This type of seek is called a "Bang-Bang" seek. In a "Bang-Bang" seek, the shape of the electric current applied to the positioning mechnism closely resembles a square wave which contains high frequency harmonics component, thereby stimulating mechanical resonance. The excitation of mechanical resonance increases both seek acoustic noise and head settling time by residual vibration.
As described in the previous paragraphs, SilentSeekTMÂ technology is designed to minimize the mechanical excitation generated by any resonance, virtually eliminating the source of seek acoustic noise..
To accomplish this, SilentSeekTMÂ technology incorporates a performance optimized sinusoidal seek trajectory, as opposed to traditional "Bang-Bang" seek profile. This prevents excitation by high frequency harmonics, while still providing minimal positioning and head settling times. The position trajectory and velocity trajectory required to achieve the sinusoidal acceleration are calculated by a Digital Signal Processor (DSP) using a recursive sine wave generation algorithm.
SAMSUNG's internal measurements have demonstrated that by incorporating SilentSeekTMÂ technology, approximately 4dBA reduction of seek acoustic noise (sound pressure level) is achieved. Figure 1 illustrates the snapshot comparison, before and after SilentSeekTMÂ technology implementation.
FIGURE 1. ACOUSTIC NOISE (SOUND PRESSURE LEVEL) COMPARISON, BEFORE AND AFTER SILENTSEEKTM TECHNOLOGY IMPLEMENTATION
ACOUSTIC MANAGEMENT (AAM):
One of the HDD industry's other efforts to reduce acoustic noise is to implement an Automatic Acoustic Management, or AAM feature. Typically, implementation of AAM feature reduces seek acoustic noise of a HDD by slowing down seek speed and consequently reducing the bang-bang excitations. SAMSUNG has been supporting the AAM feature since the 5400 RPM V20400 Series products.
While AAM feature provides the best seek acoustic noise reduction, it can also cause benchmark performance degradation of the drive curtailed by the elongated seek. According to SAMSUNG's evaluation, the benchmark data transfer performance in quietest AAM mode is degraded approximately by 3% - 5% from that of a drive using only SilentSeekTMÂ technology, while overall seek acoustics is reduced by only 0.05 bel - 0.1 bel (average sound power). Therefore, the benefits of SAMSUNG's SilentSeekTMÂ technology can virtually outshine those of AAM feature.
SAMSUNG HDD is committed to the requirements and satisfaction of its customers. NoiseGuardTMÂ , SilentSeekTMÂ , and even AAM are just a few examples of the design enhancements SAMSUNG has implemented in its SpinPoint HDD products to meet customers' ever changing needs and to support new applications.
In summary, SAMSUNG's proprietary SilentSeekTMÂ technology, when combined with NoiseGuard;TM technology, provides the best combination of low acoustics and HDD performance, ideal for today's diverse and demanding HDD applications.
