A compandor digitises the signal or not?

I consider audio in hi-fi VHS. A compandor digitises the audio signal or does it perform the compression in an analogue scheme?
Companding - Wikipedia, the free encyclopedia

Like everything else, you can do it either way. You can buy (or used to be able to buy) a single chip that would do analog companding.

barry said:

Like everything else, you can do it either way. You can buy (or used to be able to buy) a single chip that would do analog companding.

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do you see a reason why on s-vhs and vhs-hifi one would want to digitize an analogue signal, then apply this compression process , then re-convert it to analogue and finally write it on the tape, rather than applying directly analogue "compression"?
I am trying to find if this attached recorder does it analogue.

The only reason I could explain is that it's more cost-effective to perform the function digitally. There's probably a LOT more processing than just companding being done to the signal; the user's manual is not going to tell you anything about that.

Are you sure it has a compandor?

Most VCRs have ALC which isn't quite the same thing. I worked with VCRs for many years and I never came across one with signal compression as such. ALC was always done in the analog domain, usually with a simple rectifer and voltage controlled amplifier.

Brian.

No I have no idea. The video manual is the attached, it is a proffessional model.
What I have read in wikipedia about hi-fi vhs anf s-vhs (which uses the same audio format), does not say anything about digitising the signal.

"The electronic circuit that does this is called a compandor and works by compressing or expanding the dynamic range of an analog electronic signal such as sound. One variety is a triplet of amplifiers: a logarithmic amplifier, followed by a variable-gain linear amplifier and an exponential amplifier. Such a triplet has the property that its output voltage is proportional to the input voltage raised to an adjustable power. Compandors are used in concert audio systems and in some noise reduction schemes such as dbx and Dolby NR (all versions)."

So I guess this vcr uses an analogue scheme...?
If I open the vcr and I do not see any big-number-pins chip inside (except for the display and controls), I think this could confirm this?

Almost all compandor/expander systems use either NE571 or NE572 IC's from Philips although there are no doubt other manufacturers too. The trouble with compressing the audio is that an identical decompressor (expander) must be used to play it back and this would cause compatibility problems between VCRs.

It's far more likely it has a simple ALC control. the gain of the audio input amplifier being adjusted to hold the output within acceptable levels. This is what normal VCRs do.

The difference is in the timing, a compresor acts on the instantaneous audio level, it will normally adjust the gain down to cycle level and gradually increase or decrease the height of individual AC cycles to boost lower levels and shrink higher ones. The idea is to pack more audio into the available headroom and to better utilize low volumes so the signal to noise ratio is increased. The drawback is the need to do exactly the reverse when recovering the audio or it sounds very distorted. ALC on the other hand, uses a long time constant, sometimes several seconds and tracks the volume envelope rather than cycles. It is much easier to implement and although it does slightly distort the overall sound, it requires no extra circuits to play it back.

Brian.

It's far more likely it has a simple ALC control.

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Referring to VHS video recorder documentation is better than guessing in this case.

Neazoi has been referring to HiFi VHS. It uses direct recorded standard tone for backward compatibility, usually involving ALC on the recording side. The two Hifi channels are FM recorded and implementing dynamic compression. I have a Grundig VPT240 which uses a Rohm BA7703 for the HiFi audio part. It's an anlogue chip, as assumed.

The VHS HifI compression scheme is most likely defined in a standard, the chip datasheet or VCR manual isn't very detailed in this regard.