Enhancers, Exciters, etc.

[PDP]

I just bought a Focusrite VoiceMaster. It has a section called "Vintage Harmonics" which the company describes as a technique started in the 70s of recording a vocal with the dolby "On" and playing it back "Off" does this actually add 2nd and 3rd order harmonics or is it really just a treble boost? Also, is it correct that tubes add even harmonics and tape saturation adds odd order?

 

[SouthSIDE Glen]

Adding or boosting of harmonics *is* a type of higher frequency boost, in it's own way.

Assuming that Focusrite is referring to the consumer Dolby NR systems, they worked by "pre-emphasizing" the treble frequencies - i.e. they boosted high frequencies when recording. Then by "de-emphasizng" (cutting) those frequencies on playback, they ostensibly returned the HF levels to normal while cutting the added tape hiss in the process.

As such, Dolby did not care about harmonics, odd or even. If something was of high enough frequency, whether it was a harmonic, a fundamental, or a transient, it worked on it.

G.

 

[Ethan Winer]

the company describes as a technique started in the 70s of recording a vocal with the dolby "On" and playing it back "Off" does this actually add 2nd and 3rd order harmonics or is it really just a treble boost?

To add to Glen's reply, Dolby does not add harmonics in the way an Aphex Aural Exciter does. But it's not simple "emphasis / de-emphasis" either, which is treble boost when recording and cutting when playing back. Analog tape recorders already do that (NAB or IEC). Rather, Dolby applies EQ boost (and cut) dynamically, similar to how a compressor works. So a more appropriate plug-in parallel would be a multi-band compressor set to compress highs only (Dolby B) or several bands independently (Dolby A).

--Ethan

 

[PDP]

Hi, Thanks, that answers it. Just curious, how does an Aurel exciter work ? I've read tube overdrive adds harmonics but I know aurel exciters are some kind of circuitry. Does it just emulate tube drive or was it a novel invention when it came out ?

 

[SouthSIDE Glen]

For even a little more clarification, Dolby NR is *kind of* like a multi-band compressor, but differs in the detail that it performs upward compression in the encoding (pre-emphasis) stage, as opposed to the downward compression of a typical MBC. Also, I rather doubt - though I cannot rightly say for sure - that Focusrite would be emulating pro Dolby A encoding with their setting, but rather more likely the early consumer Dolby B, as that is the one far most commonly used with the decode off on encoded cassettes.

As far as how exciters work, it depends upon the brand. Aphex lets you select a reltively high frequency band and then uses a non-linear algorithm to add/boost some low-order (2nd and 3rd mostly) harmonics for that part of the spectrum, and compress those harmonics for further emphasis, and then add those back to the original signal. While tubes do add their distortion non-linearly also, it is not really a tube emulation.

BBE uses dynamic equalization (not completly unlike Dolby) and also plays with phase alignment of the enhanced part of the signal in relation to the original.

There are others that all pretty much circle around those basics of dynamic EQ, harmonic enhancement and/or phase realignment in various combinations and ways that allow them not to step on each other's patents.

G.

 

[PDP]

I rather doubt - though I cannot rightly say for sure - that Focusrite would be emulating pro Dolby A encoding with their setting, but rather more likely the early consumer Dolby B, as that is the one far most commonly used with the decode off on encoded cassettes.

G.

Thanks, Thats what one would think, but Focusrite describes it as a trick used by professional producers in the 70s. I didnt even think reel to reel multitrack machines came with Dolby, which is why I was confused by what they're saying this unit does. Anyway, Thanks for the insight.

 

[SouthSIDE Glen]

Thanks, Thats what one would think, but Focusrite describes it as a trick used by professional producers in the 70s. I didnt even think reel to reel multitrack machines came with Dolby, which is why I was confused by what they're saying this unit does. Anyway, Thanks for the insight.

Did they say "producers" or "producahs"?

You're right, if they specified pro open reel usage on the 70s, they probably are talking Dolby A, as B was not found very often (if at all) on OR decks, and C and SR were not around at all in the 70s. But I gotta say that for most quality OR decks, the idea of "enhancing" by playing back Dolby A encoding undecoded seems kind of unnecessary to me. To each their own, I guess.

G.