page 5 – 72
VP-8IP / Sep 2013
V P - 8
i P
P R O C E S S M O D E S
AM-HD
aconventionallimiterwiththecontrolcalibrationskewedanegative0.5millisecond
becauseofthelookaheadtime.Thefullrangeis0.2mSto100mS.
Veryfastattacktimescanaffordveryaccuratepeakcontrolbutattheexpenseof
musicalityanddynamics.Youshouldalwayschoosethefastestattacktimeconsistent
withhowyouwishtheoutputoftheprocessortosound,realizingthatadjustingthe
limiter for longer attack times will, as a consequence of those longer attack times,
allowpeakstoescapeuncontrolled.Howtheattacktimeisadjustedisalwaysatradeoff
betweentheaccuracyofpeakcontrolandthemusicalityoftheprocessor,withattack
timesettingsbelowapproximately6millisecondssoundingfarlessmusical(toour
ears)thansettingsabove6milliseconds.
Release
Controlstheprimary(fast)releasetimeofthelookahead
limiter.
Slower settings (longer release times) cause the peak
limitertorecovermoreslowlyfromlimiting;releasetimes
thataresettooslowmayallowundesirablesignalducking
to occur because the audio level remains low for too long
after a peak limiting event.
Conversely,fastreleasetimesincreasesignaldensity,butreleasetimesthatare
toofastresultinincreasedintermodulationdistortionwhichcan“muddy”thesound.
When processing for a perceptual codec we recommend release times no faster than
50millisecondsinordertominimizethegeneration(andcoding)ofclose-indifference
frequencyintermodulationcomponentsthatcanresultfromveryfastreleasetimes.
Theoverallrangeofthecontrolisfrom33millisecondsto330millisecondswith
anidealsettingformostapplicationsfallingbetween70and130milliseconds.
Delayed Release
Controlsthesecondary(slow)releaseofthelookaheadlimiter.The
Delayed Release
control has no effect unless the Delayed Release
checkboxischecked(seebelow).
WhenDelayedReleaseisengagedviathe
Delayed Release
checkboxthelimiterwill
releasethefirst3dBofgainreductionatthemainReleasesetting,withtheremainderof
the release occurring at the Delayed Release
setting.DelayedReleaseaffordsadrastic
reduction in intermodulation distortion and generally allows deeper limiting depth
withoutincurringtheusualintermodulationdistortionpenalty.
UseoftheDelayedReleasemodeishighlyrecommendedwhenprocessingaheadof
aperceptualcodec.Aswediscussedabove,veryfastlimiterreleasetimescangenerate
close-inintermodulationproductsarounddesirablesignalsandthismaydegradethe
perceivedqualityoftheaudioattheoutputofthecodecmorethanjusttheactionof
thecodecorlimitersthemselveswouldimply.
The Delayed Release
control offers adjustments between 100 milliseconds and
1.000seconds.Wecannotrecommenda
Delayed Release
settingbelowapproximately
160millisecondswhenprocessingforaperceptualcodec.Anidealsettingforthemajority
ofapplicationswillfallbetweensettingsof300and600milliseconds.