[ProAudio] HX Pro was :FeralA - Recordings released encoded with Dolby A

[Bill Whitlock]

I'd hesitate to call HX Pro a "process".  All HX Pro does is to account for the fact that HF program material tends to "bias" itself and that this HF program content, when combined with fixed ultrasonic bias results in significant self-erasure and loss of HF MOL (maximum HF level residual on the tape).  So HX Pro simply modulates the ultrasonic bias so that the combined effect of program HF bias plus ultrasonic bias remains constant.  Depending on tape and speed, it can improve HF "headroom" or maximum HF audio output level by up to 6 or 8 dB.  It doesn't change frequency response of the record/play process - except at levels where MOL/saturation is an issue. I guess it technically is a "process" but it's record side only, no "decoding" needed.
Hope that made sense. Lots of folks actually believe(d) that HX Pro was another noise reduction system. It's not of course, it's simply a way to get the most out of a given tape at high audio frequencies. Not so much an issue at 15 IPS, but really a big deal at 1-7/8 IPS - where it can make ordinary iron oxide tape perform like chrome.
Bill Whitlock



-----Original Message-----
From: Alan Garren via ProAudio <proaudio at bach.pgm.com>
To: John Chester <jkc at jkc-lab.com>; proaudio <proaudio at bach.pgm.com>
Sent: Tue, Feb 11, 2020 10:42 am
Subject: [ProAudio] HX Pro was :FeralA - Recordings released encoded with Dolby A

On 2/11/2020 10:12 AM, John Chester via ProAudio wrote:
> Why does perfect azimuth adjustment usually not produce minimum 
> interchannel time difference?  The most obvious answer is gap scatter 
> in the record head, but there are others.  Record EQ may not be 
> precisely matched, and bias setting may be different. Recording occurs 
> at a point slightly past the trailing edge of the record head gap, and 
> that distance varies as bias level changes.


This causes me to wonder if you have had to try this on an HX processed 
tape. I am only aware of one pro deck with HX Pro, the studer A820, and 
most people leave it turned off anyway. But it is there on some later 
models. (possibly on the A827 as well, can't remember)

Seems like a horror story for your process, chasing a HF modulated bias 
level.


Cheers

Alan

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