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Lexicon 20/20 AD User Manual

Lexicon user guide bit a/d converter 20/20 ad
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User Guide
20/20 AD
20 Bit A/D Converter

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Summary of Contents for Lexicon 20/20 AD

  • Page 1 User Guide 20/20 AD 20 Bit A/D Converter...
  • Page 2 Precautions The 20/20 AD is a rugged device with extensive electronic protection. However, you should observe the same reasonable precautions that apply to any piece of audio equipment: • Always use the correct line voltage. • Do not install the 20/20 AD in a closed, unventilated rack, or directly above heat-producing equipment such as power amplifiers.
  • Page 3 Failure to comply with these precautions, or with specific warnings elsewhere in these instructions violates safety standards of design manufacture and intended use of the instrument. Lexicon assumes no liability for the customer's failure to comply with these requirements. GROUND THE INSTRUMENT To minimize shock hazard the instrument chassis and cabi- net must be connected to an electrical ground.

  • Page 4: Table Of Contents

    Synchronization and Output Formatting • Alternate Modes Rear Panel Connectors ... 5 Audio Connections ... 6 Connectors • Cables Using the 20/20 AD ... 9 Analog Inputs ... 9 Termination and Grounding via Internal Jumpers ... 9 Balanced and Unbalanced Input Signals ... 12 Front Panel Adjustments ...

  • Page 5: Introduction

    This manual provides some basic information on conversion, but assumes the user will be familiar with the principles of analog-to-digital conversion, as well as with the digital audio interface formats output by the 20/20 AD. Information on specific data which may be required by any target device should be obtained from the manufacturer.

  • Page 6: Controls And Connectors

    Then plug the line cord into an AC wall socket providing voltage corresponding to the data plate on the unit. The 20/20 AD measures 19"W x 1.75"H x 13.9"D (483 x 45 x 353 mm). Make sure that the 20/20 AD is securely screwed into the rack, and that support is provided for the rear of the chassis during transport to avoid possible damage from severe mechanical shock.

  • Page 7: Front Panel Controls

    LEDs to hold at the display on level meters. highest level received. Press Also used to select alternate again to deactivate. modes. The 20/20 AD front panel controls are divided into three functional groups for conversion, compression, and synchronization/output formatting. Compressor THRESH UNBAL THRESH...
  • Page 8 20/20 AD User Guide When the compressor is off , the behavior of the level meters is determined by the settings of the 1dB SCALE, and PK HOLD switches. When the compressor is on , pressing DISPLAY will cause gain reduction (in dB) to be displayed on the two right hand meters (2-channel mode) or on all four meters (4-channel mode).
  • Page 9 Activates psychoacousti- cally optimized noise shap- ing. When activated, WIDE, 20BIT and HF will be lighted. Note that this type of dither can only be used in 2-chan- nel mode; activating will dis- able 4-channel mode and compressor functions. Lexicon...

  • Page 10: Rear Panel Connectors

    Note: In 2-channel mode 3 & 4 and 1 & 2 are identical. The input and output connectors conform to published stan- dards for professional and consumer formats. The 20/20 AD, however, provides the user-selected format at all connectors, e.g. the AES format, if selected, will be available at the consumer-type outputs, as well as at the XLR outputs.

  • Page 11: Audio Connections

    XLR Pinout — pin 2 high by convention Description Balanced RS-422 Balanced RS-422 Unbalanced 75 Consumer Digital Unbalanced 75 pin 2 high 2 = high Male 3 = low 1 = ground 1 = ground 3 = low 2 = high Lexicon...
  • Page 12 20/20 AD User Guide This interface requires balanced connections using high-quality, low-capaci- tance, controlled-impedance, data communication, twisted-shielded pair cable. Microphone cable may introduce a significant amount of jitter into the signal, causing distortion. Use commercially-available, consumer audio optical cable assemblies.

  • Page 13: Using The 20/20 Ad

    In these cases, connecting the shield of the audio cable(s) to pin 1 at both ends of the cable will cause the 20/20 AD to be grounded to the audio source through two paths: the shield of the audio cable and the safety ground or ground strap.

  • Page 14: Jumper Settings

    20/20 AD Main pc board. The configuration shown illustrates the jumper settings when the 20/20 AD is shipped from the factory.
  • Page 15 (or upper) two pins. (Note that the jumpers in J13 have only two pins; to open, simply remove the shunting block.) Analog Jumpers Note that the 20/20 AD’s analog inputs are not transformer isolated. It is, therefore, necessary to have one ground connection between the 20/20 AD and the audio source.

  • Page 16: Balanced And Unbalanced Input Signals

    2. If the source's isolation transformer has a center-tapped output, ground the center tap. 3. Reduce the signal level into the 20/20 AD and make it up with the front panel gain control(s). 4. Remove the power cord, open the 20/20 AD, and short out R4, R28, R54 and R95.

  • Page 17: Front Panel Adjustments

    16 bits. When the 4 CHAN switch is off, the 20/20 AD only converts CH1 and CH2, buts adds 12dB (2 bits) to the dynamic range. Your selection of mode depends primarily on how many channels you need to digitize, and on whether or not you need the extra dynamic range.

  • Page 18: Synchronization And Sample Rate

    Word Clock, you should open the leftmost jumper on J13 on all units except the last one in the chain. If an alternative ground path exists between the word clock generator and the 20/20 AD,W16 can be opened to prevent a ground loop.
  • Page 19 20/20 AD User Guide The 20/20 AD is shipped configured for Internal mode. To operate in External mode, press EXT SYNC until the desired sync source (WC or AES) lights. If the selected sync source light flashes and the PRES light is not on, it indicates that there is no signal present as a sync source.

  • Page 20: About Dither

    “nicer sounding” noise. If the recorder or workstation which follows the 20/20 AD is capable of recording or processing 20 bits, the DITHER switch should be set to 20 BIT. If, however, the equipment can only record or process a 16-bit signal, either WIDE or HF dither should be selected.
  • Page 21 -130.0 -140.0 -150.0 -160.0 2.00k 4.00k 6.00k 8.00k 10.0k 12.0k Plot of noise + distortion vs. frequency for the 20/20 AD in 2- channel mode with a -60dBfs sinewave at 1kHz. -60.00 -70.00 -80.00 -90.00 -100.0 -110.0 -120.0 -130.0 -140.0 -150.0...

  • Page 22: Automatic Offset Removal

    Until you become comfortable with the operation of the rest of the 20/20 AD, you Compressor Modes should keep the compressor turned off. Make sure that the DISPLAY, LINK and ON buttons in the compressor block are all off (unlighted) and the compressor gain knob is set to 0dB.
  • Page 23 20/20 AD User Guide Note that the 6dB GAIN setting is given only as an example. Feel free to experiment with any level in this mode. (GAIN settings above 12dB are not available because at that point practically all of the dynamic range of the converter will fit onto 16-bit media.
  • Page 24 Using the 20/20 AD -3dB 1.50:1 3.00:1 4.00:1 -6dB 1.20:1 1.50:1 2.00:1 -8dB 1.14:1 1.33:1 1.66:1 -10dB 1.11:1 1.25:1 1.42:1 -12dB 1.09:1 1.20:1 1.33:1 -14dB 1.07:1 1.16:1 1.27:1 -16dB 1.06:1 1.14:1 1.23:1 -18dB 1.06:1 1.12:1 1.20:1 -20dB 1.05:1 1.11:1 1.17:1 -22dB 1.05:1...
  • Page 25 20/20 AD User Guide When RELEASE is set to 0, the compressor acts like an amplifier with a non- linear transfer function. For example, setting GAIN to 6dB and THRESHOLD to -14dB produces a close approximation of a generic tape saturation curve. This mode is also useful for overload protection of some types of percussive instruments.
  • Page 26 (or other repeatable source) to the digital domain. To do this: 1. Do a dry run of the loudest section(s) of the tape through the 20/20 AD to check the level. Using 1dB SCALE and PK HOLD, adjust the input level until the peak comes within 6dB of clipping.

  • Page 27: Digital Audio Outputs

    W27. If the shield is connected to ground at the receiver end, these jumpers should be opened. Note that, because of the transformer or optical isolation, it is not necessary to connect the ground between the 20/20 AD and the equipment receiving the digital audio data, regardless of which output type you choose.

  • Page 28: Realigning Two Dat Recordings

    3 from channel 1 and adjusting the offset until the click disppears. The 20/20 AD includes a digital sinewave generator which is accurate to 20 bits, with a dynamic range of more than 120dB. This generator is useful in testing the digital outputs.

  • Page 29: Definition Of Terms

    : the appearance of harmonics of the input signal at the output of a device. link : the tying of two channels of the 20/20 AD compressor to a shared gain curve. lock : two or more audio signals which have the same frequency and phase.
  • Page 30 : the appearance of harmonics of the input signal at the output of a device. link : the tying of two channels of the 20/20 AD compressor to a shared gain curve. lock : two or more audio signals which have the same frequency and phase.
  • Page 31 3 Oak Park Bedford, MA 01730 USA Tel: 781-280-0300 Fax: 781-280-0499...

This manual is also suitable for:

20 ad - rev20 bit a-d converter - rev20 - rev 2

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