MicroDAC IV PORTABLE PROGRAMMABLE DIGITAL FILTER USER’S MANUAL DIGITAL AUDIO CORPORATION A DRI COMPANY
MicroDAC IV PORTABLE PROGRAMMABLE DIGITAL FILTER User’s Manual October 27, 1999 Document Number 990395 DIGITAL AUDIO CORPORATION A DRI Company 5121 Holly Ridge Drive Raleigh, NC 27612 Phone: 919 782 6767 Fax: 919 782 6766 sales@digitalaudiocompany.com www.digitalaudiocompany.com Copyright © 1999 by Digital Audio Corporation. All rights reserved.
TABLE OF CONTENTS 1.0 OVERVIEW ...............................................................................................................9 1.1 Introduction............................................................................................................9 2.0 Minimum Hardware Requirements ......................................................................10 2.0 OPERATION............................................................................................................11 2.
LIST OF FIGURES AND TABLES Figure 1: MicroDAC IV Panels.......................................................................................11 Figure 2: Basic Enhancement Setup .............................................................................13 Figure 3: 1CH MODE Block Diagram ............................................................................13 Figure 4: 2CH MODE Block Diagram ............................................................................
1.0 OVERVIEW 1.1 Introduction The MicroDAC IV is a portable, programmable digital filter targeted for applications requiring unattended filter deployment.
2.0 Minimum Hardware Requirements NOTE: Computer is required only for programming the MicroDAC IV; it is not required for standalone operation.
2.0 OPERATION MicroDAC IV promotes ease-of-use by reducing the number of buttons and switches the user needs to learn. All of the settings that required adjusting internal DIP switches in the previous version can now be accomplished using a computer. The user configures the filter(s) as desired using special Windows software, then downloads the settings to the MicroDAC IV where they are stored in non-volatile memory. The following section discusses the connections and controls for the unit.
• The INPUT LEVEL rotary knobs adjust the input signal levels on the LEFT (PRI) and RIGHT (REF) channels. Above each knob is a tricolor Level LED that indicates input signal strength. Adjust the LEFT and RIGHT INPUT controls so that the tricolor LEVEL LEDs display green or occasionally yellow. Do not allow the input level to go into the red region or distortion may occur. • The CLEAR button is used to restart the adaptive filters as deemed necessary.
2.2 Fast Start Figure 2: Basic Enhancement Setup Fast start the MicroDAC IV as follows using Figure 2 as a guide: 1. Connect the audio source(s) to the LEFT (PRI) and RIGHT (REF) ANALOG INPUT RCA jacks on the MicroDAC IV rear panel as shown in Table 1.
green. If these LEDs flash in the red color region, then the knob has been turned too far; reduce the corresponding INPUT LEVEL knob setting. Now adjust the PHONES knob to a comfortable listening level. NOTE: If the 2CH Adaptive filter is used, it is recommended that the RIGHT (REF) input be set to a slightly higher level than the LEFT (PRI) input to ensure maximum cancellation. 5. Rotate the MODE switch to the desired filter position. 6.
3.0 STANDARD FILTER CONFIGURATIONS 3.1 Selecting the Correct Filter Mode The filters in the standard MicroDAC IV are optimized for noise cancellation to increase voice intelligibility. Simple noises (e.g., tones, hum) are generally greatly attenuated. However, more complex noises (e.g., ambient restaurant noise, bar noise) may not be as effectively attenuated, but should be somewhat reduced.
Finally, always use good quality, fresh tapes for all recordings, and if possible, monitor the recording as it is being made. 3.3 Factory Preset Filter Descriptions 1CH MODE: Figure 3: 1CH MODE Block Diagram Notice that in 1CH MODE, only the LEFT (PRI) input gets processed. This signal is first fed through the Limiter, which helps prevent the signal from distorting on overload.
Table 3: 1CH MODE Second Stage Factory Presets Parameter Filter Size Prediction Span Delay Adapt Rate Adapt Mode Output Algorithm Crash Detect Preset Value 512 taps 2 samples 32 Auto Residue LMS Enabled Next, the signal is 200Hz Highpass filtered, to remove any low frequency noises that may remain after processing, and 3200Hz Lowpass filtered to remove high frequency hiss. Finally, a 10dB AGC is applied to correct for near party / far party talkers, and to provide a good output level for recording.
from a concealed microphone that has interfering radio/TV audio. The RIGHT (REF) input is the noise reference, usually the audio output from a second radio/TV tuned to the same channel. The signals are first fed through the stereo Limiter, which helps prevent the signals from distorting on overload. The Limiter internally “links” the two channels, such that an overload on either input channel will cause the levels to be reduced equally on both channels.
1CH•ST MODE: Figure 5: 1CH ST MODE Block Diagram Notice that in 1CH•ST MODE, both the LEFT (PRI) and RIGHT (REF) inputs get fed into the processor. These are usually the stereo output signals from either a stereo microphone preamplifier or a stereo body wire receiver. The signals are first fed through the stereo Limiter, which helps prevent the signals from distorting on overload.
Next, the signal is 200Hz Highpass filtered, to remove any low frequency noises that may remain after processing, and 3200Hz Lowpass filtered to remove high frequency hiss. Finally, a 10dB AGC is applied to correct for near party / far party talkers, and to provide a good output level for recording. 3.4 Programmable Filter Descriptions Filter modes A-D are factory preset as large, single 2CH Adaptive filters. Their settings are listed in Tables 7-10.
Table 9: Programmable MODE C Factory Presets Parameter Limiter Filter Size Delay Channel Delay Adapt Rate Adapt Mode Output Algorithm Reference Compensation Crash Detect 200 Hz Highpass Filter Lowpass Filter AGC Preset Value Enabled 3600 taps Input (Primary) 100 samples 16 Auto Residue LMS Enabled Enabled Enabled 3200 Hz Cutoff Disabled Table 10: Programmable MODE D Factory Presets Parameter Limiter Filter Size Delay Channel Delay Adapt Rate Adapt Mode Output Algorithm Reference Compensation Crash Detect
5.0 CALIBRATION AND SERVICE The MicroDAC IV is designed to make calibration unnecessary. However, future firmware upgrades will enhance the present capabilities of the MicroDAC IV. The firmware upgrades will be carried out over an RS-232 link in a similar way to the filter download, using special Windows software to be made available by DAC. If service is needed, please contact Digital Audio Corporation for assistance.
6.0 MICRODAC IV SPECIFICATIONS 6.1 Analog Line Inputs ·-29dBm to +14dBm, panel adjustable, Zin = 11k ·Rear panel RCA connectors Line Outputs ·+5dBm, Zout = 50 ohms ·Rear panel RCA connectors ·S/PDIF Digital Output (44.1kHz) Phones Output ·Suitable for stereo headset ·Front panel volume control and 3.5 mm stereo phones jack · Analog Conversion ·24-bit sigma-delta A/D and D/A ·12 kHz sample rate ·35Hz to 5.
