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SB3231 Folha de dados(PDF) 9 Page - ON Semiconductor |
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SB3231 Folha de dados(HTML) 9 Page - ON Semiconductor |
9 / 18 page RHYTHM SB3231 www.onsemi.com 9 Reduction algorithm efficiently removes a wide variety of types of noise, while retaining natural speech quality and level. The level of noise reduction (aggressiveness) is configurable to 3, 6, 9 and 12 dB of reduction. FrontWave Directional Microphones The FrontWave feature is implemented in two front−end modes on Rhythm SB3231: static directional and two−microphone omnidirectional. Both these front−end modes are designed to operate using two closely spaced omnidirectional microphones connected to the VIN1 and VIN2 inputs. In static directional mode, FrontWave synthesizes a directional response pattern by delaying the rear−microphone signal and subtracting it from the front microphone signal. Various microphone response patterns can be obtained by adjusting the rear−microphone time delay. In two−microphone omnidirectional mode, FrontWave synthesizes a secondary omnidirectional response pattern by delaying the front microphone signal and adding it to the rear microphone signal. The resulting omnidirectional microphone signal possesses a noise floor that is approximately 3 dB lower than that provided by a single microphone (assuming both microphones have similar noise floors). The FrontWave feature includes three parameters that can be set via external software: time delay, rear−microphone compensation filter and a low−frequency boost filter intended for static directional mode. Time delay can be configured using IDS software. It determines the polar patter in static directional mode and accounts for microphone spacing in two−microphone omnidirectional mode. The rear−microphone compensation filter provides a means to adjust the rear−microphone sensitivity so that it can better match the front microphone. It is controlled automatically through Cal/Config software. The low−frequency boost filter compensates for the 6 dB/octave roll−off in frequency response that occurs in directional mode. The amount of low frequency equalization is programmable through IDS. NOTE: For optimum FrontWave operation, ON Semiconductor recommends using matched microphone pairs. The time delay implemented using FrontWave is not explicitly limited within the system. Optimum accuracy is obtained, however, for smaller time delays. For example, in 32 kHz operation, a time delay of 81.5 microseconds can be achieved with a maximum deviation of 5% over a bandwidth of 0 to 4 kHz. This allows a microphone port spacing of approximately 28 mm. For 16 kHz operation, a similar accuracy is observed for a time delay of 78.1 microseconds, corresponding to a port spacing of approximately 26.8 mm. Smaller time delays can be implemented with improved accuracy. Volume Control, Trimmers and Switches External Volume Control The volume of the device can either be set statically via software or controlled externally via a physical interface. Rhythm SB3231 supports both analog and digital volume control functionality, although only one can be enabled at a time. Digital control is supported with either a momentary switch or a rocker switch. In the latter case, the rocker switch can also be used to control memory selects. Analog Volume Control Both the external (analog) volume control and trimmers work with a three−terminal 100 k W − 360 kW variable resistor. The volume control can have either a log or linear taper, which is selectable via IDS. It is possible to use a VC with up to 1 M W of resistance, but this could result in a slight decrease in the resolution of the taper. Trimmers The trimmer interface provides the ability to control up to 19 hearing aid parameters through up to four trimmers. A single trimmer parameter can have up to 16 values and a single trimmer can control multiple parameters (e.g., Trimmer 1 can control compression ratio in all four channels simultaneously). The trimmer must be three−terminal 100 k W to 360 kW variable resistors and have a linear taper. Parameters that can be assigned to trimmers include Noise Reduction, Low Cut, High Cut, Compression Ratio, Wideband Gain, Tinnitus Noise Level, Crossover Frequency, Lower Threshold, Upper Threshold, EQ Gain, Squelch Threshold, High Level Gain, Low Level Gain, AGC−O Threshold, Static Volume Control and Peak Clipper Threshold. NOTE: There may be limitations to which parameters can be used together. Digital Volume Control The digital volume control makes use of two pins for volume control adjustment, VC and D_VC, with momentary switches connected to each. Closure of the switch to the VC pin indicates a gain increase while closure to the D_VC pin indicates a gain decrease. Figure 7 shows how to wire the digital volume control to Rhythm SB3231. Figure 7. Wiring for Digital Volume Control D_VC VC GND |
Nº de peça semelhante - SB3231 |
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Descrição semelhante - SB3231 |
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