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Benchmark AD2402-96 Operating Manual

Ad2k+ two channel, 96-khz analog to digital converter
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BENCHMARK MEDIA SYSTEMS, INC.
AD2402-96 / AD2K+ TWO CHANNEL, 96-kHz
ANALOG TO DIGITAL CONVERTER
11/09/04 Revision - Absolute Input Polarity Correction pg. 17
Operating Manual

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  • Page 1 Revision BENCHMARK MEDIA SYSTEMS, INC. AD2402-96 / AD2K+ TWO CHANNEL, 96-kHz ANALOG TO DIGITAL CONVERTER 11/09/04 Revision - Absolute Input Polarity Correction pg. 17 Operating Manual...
  • Page 2 A D 2 4 0 2 - 9 6 - A N A L O G T O D I G I T A L C O N V E R T E R Operating Manual © BENCHMARK MEDIA SYSTEMS, INC. 5925 Court Street Road Syracuse, NY 13206-1707 Phone (315) 437-6300•...

  • Page 3: Table Of Contents

    T able of Contents Digital Input Connectors System Overview “In” Connector Sample Rate “Loop” Connector Word Length Digital Outputs Digital Audio Reference Using the Meters Digital to Digital Processing Digital Outputs Using the Peak Hold Function 88.2 and 96 kHz Operation Selecting Meter Range “Dual Cable”...
  • Page 4 NN™ or NS™ Processes in Cascade Why NN3™ for Cascaded 16-bit? Dither Will Dither Damage My Speakers? How is the Performance Measured? Avoid Truncation without Dither Digital Word Length Increases… Additional Information Word Length Reduction Curves...

  • Page 5: System Overview

    A unique feature of the AD2402- 96 allows simultaneous 24 and 16-bit outputs. Digital Audio Reference A digital audio input jack allows the AD2402-96 to phase-lock to an external AES or SPDIF digital audio reference. Most 2-channel applications will not require an external reference However, the external and many users will never need to use the external reference input.

  • Page 6: Digital To Digital Processing

    SCMS override, and 75 ohm unbalanced to 110 ohm balanced conversion. The D-to-D feature also allows the AD2402-96 to act as a 1 in 4 out digital distribution amplifier! For processing a 24-bit signal down to 16-bit, as would be the case in mastering a CD or producing a DAT tape, the user can take the 24-bit signal into the AD2402-96 digital input.

  • Page 7: Dual Cable" 88.2 And 96 Khz Modes

    A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L “Dual Cable” 88.2 and 96 kHz Modes “Dual Cable” 88.2 and 96 kHz modes provide a means for recording at sample rates up to 96 kHz on equipment that was originally designed for 48 kHz.

  • Page 8: Single Cable" 88.2 And 96 Khz Modes

    For more information on proper cable wiring to receive a signal from an unbalanced source, known as forward referencing, see page 15 of the Benchmark Media Systems, Inc. application note: “A Clean Audio Installation Guide”.

  • Page 9: Power Supply Connection

    Power Supply Connection The AD2402-96 is equipped with an industry standard 4-pin XLR power connector, and may be powered from a 12 V battery, or from an external DC power supply. The input voltage should be between 11 and 18 VDC.

  • Page 10: Front Panel

    “Low Battery” LED The AD2402-96 is equipped with a red “Low Batt” LED. The low-battery light is calibrated for use with 12-volt lead-acid “gel-cell” batteries but may be adjusted for use with other types of batteries. Lead-acid batteries should be charged shortly after the “Low Batt.” LED turns on. Note...

  • Page 11: Input Level" Switch

    +14 dBu. The “Input Level” switch should be set so that the AD2402-96 will clip 3 to 6 dB before the microphone preamplifier. For example, if your microphone preamp has a maximum output level of +24 dBu, then set the switch to “+20”.

  • Page 12: Lock" Led

    Therefore, avoid microphone preamps that cannot achieve at least +16 dBu out, without clipping. Even then the dynamic range of the preamp and not the AD2402-96 will, in all probability, be limiting the dynamic range of your high-quality 24-bit recordings.

  • Page 13: Word Length Mode" Switch

    For typical A/D conversion applications, select either “44.1” or “48”. If an external digital audio reference is connected to the “Digital Input”, the AD2402-96 will automatically switch from internal to external clock, and the “Lock” LED will turn on. A feature unique to Benchmark...
  • Page 14 “D-to-D” functions include; word length reduction, SPDIF to AES/EBU format conversion, AES/EBU to SPDIF format conversion, and SCMS copyright correction. In addition, the AD2402-96 can act as a 1-in, 4-out digital distribution amplifier. The digital input will accept either consumer or professional format digital audio. The “Format”...

  • Page 15: Meter Scale" Switch

    A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L If the “Word Length” switch is set at “24”, the “D-to-D” mode Important Note: will alter the status bits but will not alter audio data bits. All other “Word Length” settings will add dither noise to the audio.

  • Page 16: Digital Led Meters

    “FSD” LED. Short single-sample digital clipping events are often audible, and all “FSD” events should be avoided. The AD2402-96 has a very large dynamic range (especially when operating at 24-bit output word lengths). It is wise to use some of this dynamic range to provide more headroom as insurance against clipping.

  • Page 17: Format" Switch

    A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L “Format” Switch The two-position “Format” switch controls the format of the digital outputs. The “AES” position sets the status bits to professional (AES-3) format.

  • Page 18: Rear Panel

    (0 dBFS). PLEASE NOTE: An internal absolute polarity inversion error was discovered some time after the creation of the AD2402-96/AD2K+. The following table is revised from the original and should be used instead of the original table.

  • Page 19: Dc Power Input

    Pins 2 and 3 are not connected internally. Fuse The AD2402-96 is equipped with a 2-Amp fuse. This fuse is designed to blow if the AD2402-96 is connected to improper voltages and/or in reverse polarity. It is important to use an exact replacement.
  • Page 20 SCMS override, and 75 ohm unbalanced to 110 ohm balanced conversion. The D-to- D feature also allows the AD2402-96 to act as a 1 in 4 out digital distribution amplifier. In most 2-channel recording applications it is not necessary to connect a signal...

  • Page 21: Loop" Connector

    Or, one digital-audio source can be looped through one or more AD2402-96 converters to provide a large digital-to-digital fan out for dubbing. If the loop feature is not being used, a 75-Ohm termination should be connected to the “Loop”...

  • Page 22: Using The Meters

    (7.8 msec) decay time constant. Selecting Meter Range The AD2402-96 has two meter ranges; one with 6-dB steps, and one with 1-dB steps. The 6-dB scale allows monitoring for signal presence, as well as coarse adjustment of levels. The 1-dB scale allows highly accurate adjustment of digital levels.

  • Page 23: Fast Decay Time-Constant

    LED light up for one sample of a 44.1 kHz or 48 kHz clock. Therefore, the meters on the AD2402-96 incorporate a decay time constant which extends the on-time of all LEDs, and a second slower time constant which extends the on time of the highest LED triggered by a peak.

  • Page 24: Fsd" Meters

    A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L Chapter “FSD” Meters What is “FSD”? There are several different ways of labeling the clip LED on a digital meter. These include; 0 dBFS, Clip, Over, and FSD.

  • Page 25: The Fallacy Of "Over" Indicators

    A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L The Fallacy of “Over” Indicators “Over” indicators are based upon the assumption that a digital clip cannot be heard if it has a duration of three or less consecutive samples.
  • Page 26 A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L In spite of our best efforts to produce clean audio, there is always a demand for a CD that is as loud or louder than other CDs.

  • Page 27: Design Philosophy

    AD2402-96R was designed by John Siau, Allen H. Burdick, and Ralph Henry at Benchmark Media Systems, Inc. It is carefully engineered to reliably provide the highest possible audio transparency. We have not tried to add “warmth” or “color” to the audio.

  • Page 28: Specifications

    A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L Appendix Specifications Sample rates = 44.1, 48, 88.2, 96 kHz, and variable THD + N = -107 dBFS (0.00033%) at -1 dBFS Dynamic range = 117 dB, A weighted...
  • Page 29 A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L NN™ NS™ OISE UILDUP VS UMBER OF ASSES NN™ NS™ C OISE UILDUP URVES UMBER OF ASSES...
  • Page 30 A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L...

  • Page 31: Jitter And It's Effects

    For that reason, great effort has been invested eliminating sample clock jitter in the Benchmark A-to-D converters. A unique and proprietary Phase Lock Loop keeps the converters virtually free from sample clock jitter, under all operating conditions.

  • Page 32: Why So Low

    The FFT analysis shown in Figure 4 demonstrates the ability of the AD2402-96 to resolve tones as low as -140 dBFS. Note that in this test, the AD2402-96’s highest jitter induced side bands occur at 4 kHz and 6 kHz. These each measure at an extremely low -140 dBFS and indicate that jitter at 6 kHz (a common problem frequency) is below 5 Pico-seconds.
  • Page 33 Jitter modulates the time interval between samples, and this can radically alter the response of the filter. For example, if converter clock in the AD2402-96 were derived directly from the AES/EBU receiver (as it is in many converter products) the stopband attenuation at 100 kHz would be degraded from 117 dB to only 28 dB.

  • Page 34: Additional Information

    A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L 6. 26 IGURE TOP BAND TTENUATION VS ITTER AT THE ONVERTER Additional Information Additional information about jitter may be found at the following locations. http://www.nanophon.com/audio/jitter92.pdf Jitter: Specification and Assessment in Digital Audio Equipment By Julian Dunn Presented at the 93...

  • Page 35: Word Length Reduction

    Appendix Word Length Reduction The AD2402-96 is equipped with two state of the art world length reduction systems: The Benchmark NN™ (Near Nyquist) system, and the Benchmark NS™ (Noise Shaped) system. Unlike most competitive systems, the Benchmark NS™ system is based upon the most current psycho-acoustic models.

  • Page 36: Nn™ Or Ns™ Processes In Cascade

    NN™ and NS™ functions. While each of the Benchmark NN™ and NS™ processes have been optimized for certain levels of ambient noise contribution, it is important to point out that the processes do not rely on this noise for dithering.

  • Page 37: Why Nn3™ For Cascaded 16-Bit

    While it is desirable to keep the dither inaudible, it is also necessary to apply enough dither to fully randomize the noise added by word length reduction. The Benchmark NN™ and NS™ systems provide full randomization and are carefully designed for minimum audibility.
  • Page 38 A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L NS™ W 44.1 ENGTH EDUCTION URVES FOR The 16-bit 44.1-kHz NS3™ noise shaping, shown above, provides a 14-dB improvement over 16-bit TPDF, in terms of noise audibility.
  • Page 39 A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L NS™ W ENGTH EDUCTION URVES FOR The 16-bit, 48-kHz NS3™ has a 17-dB advantage over 16-bit TPDF. NS™...

  • Page 40: Will Dither Damage My Speakers

    20-bits. Many recording engineers have discovered that they can truncate the outputs of their A/D converters without causing distortion. Do not try this with the AD2402-96! The AD2402-96 is a very quiet 24-bit converter, and it...

  • Page 41: Digital Word Length Increases

    Instead, use the digital to digital word length reduction feature in the AD2402-96 to reduce the word length back to 16-bits. Remember every word length reduction process requires a new source of dither noise.
  • Page 42 A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L Another dither article entitled "The Secrets of Dither" authored by Bob Katz, can be found http://www.digido.com/ditheressay.html...

  • Page 43: Word Length Reduction Curves

    A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L Additional Word Length Reduction Curves NS™ W 88.2 ENGTH EDUCTION URVES FOR NN™ W 44.1 ENGTH EDUCTION URVES FOR...
  • Page 44 A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L NN™ W ENGTH EDUCTION URVES FOR NN™ W 88.2 ENGTH EDUCTION URVES FOR...
  • Page 45 A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L NN™ W ENGTH EDUCTION URVES FOR 44.1 ENGTH EDUCTION URVES FOR...
  • Page 46 A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L ENGTH EDUCTION URVES FOR 88.2 ENGTH EDUCTION URVES FOR...
  • Page 47 A D 2 4 0 2 - 9 6 O P E R A T I N G M A N U A L ENGTH EDUCTION URVES FOR...
  • Page 48 For continued fire hazard protection, fuses should be replaced ONLY with the exact value and type as indicated on the rear panel and on this page below. Do NOT substitute parts or make any modifications without the written approval of Benchmark Media Systems, Inc. Doing so may create safety hazards.

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