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  1. #8
    Senior Member
    Join Date
    May 2015
    Grosse Pointe Woods, MI
    Quote Originally Posted by Archimago View Post
    Interesting history there Arny... I assume the effect must have been transparent.
    Listening tests of this device were among our early adventures with ABX:


    "The Ampex 16 Bit Digital Delay Line vs. wire comparison was made in a professional recording studio control room on time aligned UREI 813 speakers with McIntosh MC-2100 amplifiers. The audio source was local country artist P. J. Coombes who had been recorded on a 24-track Ampex MM-1000. That tape had been mixed to a 2-track tape at 15 IPS on a Scully 280. The mixdown and playback was through an API console. Thus the master tape played for these ABX trials was of quality not available to the record buyer of the era.

    The listeners included professional recording engineers with years of experience on major label projects, professional maintenance engineers, and recording engineering students.

    For those not familiar with studio equipment, these are some of the most revered pieces of equipment of that day. API consoles are still prized today for their high quality. The studio microphone locker included Neumann U-67,Neumann, U-87, and Neumann KM-86 along with various microphones that might be selected for specific applications such as inside the drums.

    Also I presume there's an AD/DA in the device.
    For sure. It was said to be a proper 16 bit device. Its clock rate may have been adjustable in the 40-50 KHz range. The dB article that I referenced seems to be the sole surviving piece of doc that is stored in public.

    It was tested quite exhaustively, and found to be sonically transparent. Those tests is the origin of my interest in testing gear with a set of keys, jangling. This is quite demanding, and just about everything in a good studio in those days would fail to be transparent enough to pass ABX tests.


    What kind of conversion quality are we looking at with the ADD-1 back in the day for these LP's!?
    I don't have a sample to test, but from analysis of LPs that appear to be cut using it, I would speculate somewhat informedly that it used analog filters, and R2R conversion. The analog filters were relatively gentle by modern standards. The transistion band appears to be huge. A fair amount of loss in the 17-22 KHz range.

    I'm sure Michael Fremer would have no trouble identifying these digitally compro[quotemised LPs .

    I'd guess that a very high proportion of LPs that were cut from 1979 to 1989 were cut using it. IOW, during production they were digitized @ 16 bits, and were brick wall filtered at 24 Khz or thereabout. I don't beieve that he has complained about even one instance of this.

    For example, every legacy copy of the DSOTM LP probably received this treatment.

    During loud passages, the brick wall and rejection band is covered up by the nonlinear distortion that is inherent in the LP format:

    Name:  Needle drop of supertramp give a little bit  loud passage.jpg
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    This is an interesting finding to me, because it turns all of those LPs into potential test records for evaluating the nonlinear distortion inherent in the LP. If analysis of a quiet passage or leadin groove shows the indicated digial artifacts or something like them, then anything above the observed transistion band has to be generated by the LP format itself, as no such signal was ever sent to the cutter head. LPs cut in Y2K and later seem to be free of this issue - the delay may not have been used, or it was running at a higher sample rate such as 24/96.

    To clairfy, the needle drop shown is of a contemporateous Supertramp LP.
    Last edited by arnyk; 2018-01-07 at 05:58.

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