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Old 3rd April 2012, 09:03 PM   #11
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They didn't want to provide a receipt of making those CD players (DAC) for everyone. After all, it was a comercial enterprise.
They standardized just the bare minimum - the CD's...
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Old 3rd April 2012, 09:58 PM   #12
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John Watkinson's literature of the the mid 1980s gives examples of 'typical' anti-aliasing filters:
a nine-pole elliptic passive, which is -60dB down at 22kHz, and a thirteen-pole which is down -80dB. Group delay was a problem for such high order filters which needed compensation for exacting applications.
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Old 4th April 2012, 05:23 AM   #13
oshifis is offline oshifis  Hungary
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The Chesky Test CD contains tracks recorded with 128-times oversampling, and "standard" tracks for comparison. So I assume there is no standard for oversampling (and anti-aliasing) at the recording end.
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Old 4th April 2012, 09:31 AM   #14
AndrewT is offline AndrewT  Scotland
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Why are so many of the anti-aliasing and replay filtering based on odd order filters?

Is there some particular characteristic that makes them different from even order filters and of some advantage to audio?
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Old 4th April 2012, 04:33 PM   #15
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It's the way that analog filters are build. Even order filters usually would leave the output impedance unadapted with the next stage.
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Old 4th April 2012, 05:28 PM   #16
DF96 is offline DF96  England
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Quote:
Originally Posted by SoNic_real_one
They standardized just the bare minimum - the CD's
When designing a long-term system architecture standardising the bare minimum is the the best option. The CD acts as the interface between the recorder and player. By defining the interface it leaves plenty of scope for improvements in technology. This is how railways, roads, the telephone system, the internet work - define the interface, leave the rest flexible.

Sometimes people are tempted to make the interface definition flexible, with scope for future changes. My experience in IT is that this almost always fails: it creates complications, and it nearly always turns out that you soon want a change which you haven't allowed for. Examples of poor interface design: almost any Microsoft file format, which is why they create such trouble with intergenerational compatibility.
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Old 4th April 2012, 06:26 PM   #17
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by SoNic_real_one View Post
It's the way that analog filters are build. Even order filters usually would leave the output impedance unadapted with the next stage.
I don't understand your answer. Thanks for replying.
Could you explain or direct me to a site.
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Old 6th April 2012, 07:17 AM   #18
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Quote:
Originally Posted by SoNic_real_one View Post
Even from the first DAC's made by Philips and Sony, OS was seen as necessary (4x as minimum).
Well, Sony's first player (CDP-101) had no oversampling and used an analogue brick-wall filter.

Philips first player (CD100) did use 4x oversampling (with noise shaping), but this was mainly to achieve 16-bit performance from the 14-bit DAC (TDA1540).

And there were plenty of 2x oversampling filters used back in the mid-1980's (eg. Sony CX23034 used in CDP-302ES, CDP-502ES etc.)
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Old 6th April 2012, 10:45 AM   #19
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Sony used brick filter in the first product then they quicky move to OS. Is that a sign that analog brick filtering was working? Or it was just a sign that the technology wasn't capable of making fast enough DAC's to cope with an OS signal? Sony needed to have something out quick, in competition with Philips.
To process OS you need faster settling times on DAC stage. With low distortion. That needed some time to develop.

Or... why do you think they moved as fast as they did to 2x, 4x, 8x, 16x??? A conspiration to make bad sound?

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Old 6th April 2012, 01:26 PM   #20
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Fascinating chapter of industrial history. Obviously consortia contain contradictions, with each party looking to take up a differentiated position on the same bandwagon.

Sony's insistance on 44.1kHz and 16 bits was a bit last-minute. That suggests to me that there can have been no agreed exact standard for filtering during the recording process.

Perhaps Sony had less to gain from oversampling because their DACs needed a downstream audio switching stage that required stringent filtering anyway. Also, the PWM current output was timed by a clock running at over 512 times the sample rate, which was a limiting feature. In their players using the TDA1541 I think they followed Philips' practice.

Who made the machines used in the recording process? I would guess that de facto standards evolved in the industry.

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