Thank you for the link to this article.Originally Posted by Alex Nikitin
It explains in simple terms how the technology works.
I must agree that the article clearly states that HX-pro was not befor HX or even Dolby HX.
I can though supplement with the fact that B&O signed up for the patent of HX-Pro.
That must, according to the article, have been later than the patent of HX.
Dolby HX, as the licenced edition of HX-Pro have likely carried on being called, was a simplyfied and less effctive or less quality edition of the HX-Pro according to other trustworthy articles there is to be found on the net (with reference to sources like this article has in the end) as well as according to this article.
Problem is that this article also states that HX-Pro got it's name from Dolby HX.
This makes history of this technology a bit complicated.
There are machines on the market dating to the time after HX-Pro was implemented on many machines, that also have the writing of Dolby HX on them - and there are machines having the B&O patented HX-Pro writeen on them.
Another point; as it clearly states in the article you are linking to:
"This lowers over all distortion......................"
".............permitting higher recording levels and better S/N ratio without audible distortion at unexpected peaks in the audio signal"
This is the side effect I was writing about and the reason B&O at some point launched HX-Pro as a (single ended) Noise Reduction System.
From this article at some official B&O site, you can read:
"I said above that HX Pro is the only system that keeps dynamic bias constant However, the original Dolby HX circuit had many of the same properties. But the facts are that while Dolby HX restores some of the dynamic range available on cassette tape that is otherwise lost by the automatic compression mechanism referred to above, it does so in a convoluted fashion with for example a control signal derived from a Dolby B circuit, and is simply not as effective. In addition, the Dolby circuit is mono, where the B&O circuit, which works quite independently of any noise reduction circuit in the system, is a true stereo device, operating quite independently on each channel."
and furthermore:
"The HX Pro circuit is permanently connected, which is sensible enough given its function. "
This verify that HX-Pro is a better working solution than Dolby HX.
And this is also what I was told by the technical department of Bang & Olufsen at a visit.
(B&O and I are both Danish)
From another site on the web about noise reduction:
"Dolby HX Pro
Like Dolby HX not a noise reduction system per se, it's a headroom expansion system that also helps the deck to record high frequency sound without distortion when used in combination with a NR system by controlling how high frequencies are recorded onto the tape, thus enabling the noise reduction system to perform much more effectively since there is less danger of tracking errors, slightly less tape saturation effects audible as well when it's used. It can be very effective and is single ended, i.e. it needs only to be used while recording, especially effective when used with cheap ferric tapes that display an uneven HF response and in particular when recording from the radio were MPX tones interfere with the NR tracking. Not developed by Dolby Laboratories at all but by the Danish company Bang & Olufsen and it archived all that the original HX system set out to do, but it's simpler circuitry and the fact that it worked much better with cassette tape recorders than Dolby's system meant that the company gave up on it's own system and licensed the Danish system. Only available as a part of a dolby NR license and built into a recorder, it's not possible to build it into a codec."
What do you think about history of this system after being "forcing me" to spend time on reading the article you linked to, my comments and the link I gave you?
My judgement: Dolby HX and HX-Pro is not the same, although alike and although developped at about the same time.
HX-Pro is more efficient and higher quality.
HX-Pro nor Dolby HX are actually meant as a noise reduction systems even though it has noise reduction as a side effect, however, for marketing issues, HX-Pro was launched as such.
Let's get other opinions on the subject.
"dolph"
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