High-Performance Laser-Based Audio Fiber Link

with 200KHz sampling, DC-65KHz audio, ultrasonic dither


Pro-Audio Fiber-Optic Receiver

Benefits of the Pro-Audio-Fiber System:

  • DC to 65 KHz Analog Bandwidth with 200 KHz sampling

  • Digital Audio - Three Times More Bandwidth Than Compact Discs

  • 95 dB Dynamic Range

  • 16 Bit (Analog) with ultrasonic dither (20 Bit Digital)

  • 4 Channels on one fiber

  • Can be wave division multiplexed on existing Fiber Optic systems


    PLUS:


    All the Benefits of Fiber Optic Cable:

  • No Noise

  • No Hum

  • Interference Free

  • Up to 45 kilometers of cable without repeaters

  • No Licensing


    Detailed Performance:

    Audio Frequency Response:
    DC - 65 KHz, Flat To +/- 1.5 dB

    Number of Channels of Audio:
    4, plus AES/EBU option

    Time-Coincidence of Audio Channels:
    Within +/-5.0 Microseconds

    Group Delay Variation Each Channel:
    Corrected Across DC-20 KHz (standard) and correctable for composite stereo FM


    Description:

    The T-Tech AUDIO-FIBER digital audio link is a complete professional audio transmitter and receiver system for converting analog signals (95 dB dynamic range) to fiber optic signals and back again.

    Note: The digital portion of the AUDIO-FIBER system is designed for four 20-bit channels merged onto one fiber channel. The optional AES/EBU channel has its own dedicated fiber channel.


    Applications include:

    Broadcast studio-to-transmitter link, with lower loss than possible with committed point-to-point wireline and 100% immunity to interference, noise and hum pickup.

    TV Network stereo audio distribution systems with immunity to hum, interference and noise pick-up.

    Recording studio applications where signals must be transported between two locations with no degradation.

    Analog signal transportation in industrial applications (such as an instrumentation recorder) over long distances with high bandwidth and no signal deterioration.

    Industrial remote metering and control.

    Multi-channel audio distribution on fiberoptic cable for auditoriums, theaters, stadiums, etc.


    Optical Receiver Sensitivity:
    1 Microwatt

    Optical Receiver Overload Level:
    100 Microwatts

    Optical Sensitivity For One Error Per Month (removed by correction system):
    2500 Nanowatts

    Sampling Rate Each Channel:
    200 KHz

    Number of Bits Each Channel, Transmit Direction (analog signals):
    16 with SINC correction

    Number of Bits Each Channel, Receive Direction (analog signals):
    16 With Analog Filtering

    Total Harmonic Distortion Each Channel, Transmit-to-Receive at 1 KHz:
    0.007% Maximum, 0.003% Typical

    Optical Transmitter Peak Power:
    200 Microwatts (single-mode fiber)

    Optical Transmitter Wave Length:
    1300 Nanometers (810 Nanometers on Special Order)

    Error Softness Effect:

    Digital error detection is based on the double redundancy method. The result of a detected error is to cause an exponential interpolation in the receiver. Thus loud "thunder claps" are avoided and, for all practical purposes, eliminated. The quick recovery of correct data after an error is achieved by a very high 200 KHz sampling rate - almost 5 times the rate used by compact discs.

    Burst errors will cause extended holding of status quo analog level rather than a huge analog pop. This is also due to the quick system update after a short error.

    Fiber Optic Cable Length, Maximum Recommended:
    Over 45 Kilometers


    T-TECH PRO-AUDIO FIBER OPTIC TRANSMITTER-RECEIVER

    The T-TECH Pro-Audio Fiber optic link converts four channels of professional audio or other analog information having DC-65 KHz bandwidth per channel into digital information, which is then converted to optical information so that it can be transmitted across a single fiberoptic cable, then back into digital and finally again into analog.

    The optical information is generated as a pulse-code- modulated LASER signal at 1300 nanometers wavelength and 200 microwatts, suitable for driving single-mode fiberoptic cables for long distances. The pulse-code modulation format is AC-coupled. Modulation rate is 50 Megabits per second. This high rate supports error correction of all four channels.

    Error correction coding, detection and elimination are built- in features of the link. T-TECH is the only vendor known to offer this feature in a commercial digital audio fiberoptic link. The error correction feature was deemed important by the vendor because when digital audio is transmitted over fiber, the limited optical power output of the LASER cannot be considered high enough (after suffering the loss of the cable) to render receiver noise negligible.

    Typically, fiberoptic installations run bit error rates ("BER") of one per billion. That is, an error can occur in the interpretation of the signal by the receiver once per billion digital pulses. For 50 Megabits/second (50 million pulses per second), every 20 seconds an error would occur.

    T-TECH does not consider this to be adequate performance, since an error could represent a loud pop or click in the reconstructed analog signal.

    Even if total fiber losses are made smaller than the maximum loss allowable for a BER of one per billion, the error correction circuitry continues its vigil, ready to suppress errors that would potentially ruin an important audio program or analog data.

    The transmitter unit, pictured in one of the photos, has four taut-band panel meters for indicating exact peak analog signal amplitudes applied to the digital converters. Each meter can display a five (5) microsecond peak of either polarity and hold it for several milliseconds. Special damping circuits minimize mechanical overshoot in the taut-band meters, which are 2% accurate.

    The receiver unit has only one front-panel indicator, an LED, to show that a fiberoptic fault exists. This fault indication is also available as a relay-contact closure signal on the rear panel.


    Vendor contact is Dan Talbot, President, T-TECH, at:

    VOICE NUMBER (978) 562-5820

    FAX NUMBER (978) 246-0290


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