Conference hips::uk_audioo

122.0. "New "bitstream" CD-player" by TASTY::JEFFERY (What do batteries run on?) Thu Sep 07 1989 23:31

    All this talk about CD players, has brought to mind an article I read
    in HiFi News & Record Review in Basingstoke Library this Saturday.
    
    The gist of it is that Phillips have come up with a system for doing
    the D-A conversion called bit-stream, that is radically different from
    the usual method.
    
    Instead of using 14 bit or 16 bit converters, Phillips have come out
    with the bitstream player which uses only ONE bit!!
    
    Before you check the date of this note to see if it's April the 1st, I
    ought to explain what I understood.
    
    The digital representation of music, as used by CD players is taken by
    sampling the signal 44 thousand times a second, converting the
    amplitude of that signal to a value, and storing that value on the CD.
    
    The normal CD player then reads back the set of values, converts the
    values back to an analogue signal, and then off to the amp & speakers.
    CD players have two problems however: 
    
       - The amplitude of the signal is inaccurately represented, as it
    cannot hope to fully represent the continuous analogue signal. 16 bit
    players often only resolve to 14 bit accuracy, as they are not given
    enough time to be accurate to the full 16 bits.
    
       - The signal has spurious high frequency signals added to the
    original signal, due to the sampling. Various manufacturers have tried
    to combat this by "oversampling". I'm sure this is explained somewhere
    else!
    
    The bitstream player attempts to address the first point, but also
    apparently, goes a long way to addressing the final point.
    
    The bitstream player consists of a 1 bit DAC fed by a very high speed
    digital signal. For a 20% strength signal, the 1 bit DAC would give a
    high frequency signal, set high for 20% of the time. The frequency part
    of this signal is easily filtered out, miraculously leaving the music,
    with Phillips claim, none of the accuracy problems, and a lot of the
    sampling problems sorted.
    
    I must admit, I find this problem difficult to grasp, and I didn't
    understand the electronics bit of it. It's a fascinating article, and I
    can well recommend it. I look forward to hearing the player.
    
    Cheers.
    
    Mark.

    Noel Keywood did a quick review of the new Philips bit stream player
    in September's HFR.
    
    NK said it did not suffer from any of the nasties usually associated
    with CD replay, and produced a good believable sound. He said what
    limitations it had were most likely due to the player being cobbled
    together quickly for reviewers, and that he looked forward to testing
    a full production model in which these problems should be easily
    resolved.
    
    Praise indeed, especially from NK in HFR!
    
    Dave