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Dual DAC´s & Dynamic Range.

Discussion in 'AV Receivers & Amplifiers' started by Jase, Jun 3, 2002.

  1. Jase

    Jase
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    Just wondered what some of the Technical guys think about the use of two or four DAC´s (in the case of the Denon A1SE and its Pure Direct mode) to increase dynamic range and, supposedly, audio quality.

    Here´s some info that I´ve copied and pasted from a post on another forum re the Denon A1SE/AVR 5800 DAC configuration:

    "A DAC will have a specific dynamic range, measuring full scale output to the noise floor. But, a DAC that has a specific word length capability will not have a similarly high dynamic range output, i.e., a 24 bit DAC can indeed process PCM input data with up to 24 bit word length, but that DAC will not have a usable 24 bit dynamic range - dynamic range is calculated in dB as (6n) 1.76, where n=wordlength - quality 24 bit DACs typically have a dynamic range of over 100 dB, but not the same as the theoretical 144 or so dB of dynamic range that the 24 bit wordlength describes.

    So to increase the dynamic range, the designer may choose to "double up" the DAC parts, and have 2 DAC´s parallel-processing 1 audio channels output. Each DAC is operating "out of phase"with respect to the other (digitally speaking), their 2 outputs are then combined, this provides a 6db increase in gain, along with a 2db rise in noise, giving therefore a net increase of 4db dynamic range. Such a configuration is called differential mode, or differential-DAC mode. Top end outboard D/A converters often are configured with differential-DAC configuration. Our DVD-5000 dvd player was equipped with a differential-DAC output stage (2 Burr Brown PCM -1704 DAC´s per channel).

    The AVR 5800 (A1SE), in Pure Direct (stereo) mode, uses 4 DAC´s per audio channel in what is called differential-differential mode, or dual-differential mode. This provides a roughly 8db practical increase in dynamic range, compared to single DAC/channel operation - quite a substantial improvement.

    The audible result is improved very low signal level resolution. We use the Analog Devices AD-1853 DAC, a very high performance 24 bit/192 Khz part. In Pure Direct mode, the AVR 5800´s (A1SE) dual-differential operation provides improved reproduction with very wide dynamic range source material. Plus, Denon´s AL24 (ALPHA 24) DSP upsampling/interpolation algorithm is engaged, which further improves the low level resolution."

    As mentioned, what do the technical guys think and how come other manufacturers arent using the same configurations??
     
  2. garmtz

    garmtz
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    That was a very good explanation of differential/dual-differential! :)

    Indeed, these configurations can improve performance, but it still won't tell you how well an amplifier will perform soundwise. Lowering the noise floor in the pre-amp theoretically will improve dynamic range, but so will well-designed power supply sections.

    I know the Lexicon MC-12 also uses dual-differential DACs. It's best to use (dual-)differential in a balanced topology of the whole pre-amp section, so both halves of the signal will be handled independantly throughout the unit.
     
  3. Dubbing Mixer

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