Embed Size (px)
Citation preview
In audio mixing and mastering it is becoming increasinglyimportant to cover a variety of different formats and listeningconditions. The real challenge is to ensure that the mix translates
well out of the studio, i.e. for Domestic, Broadcast or Film Theatreaudiences; in mono, stereo and 5.1.
While this challenge can be approached in various waysdepending on resources and facilities, one way is simply to simulatereal cinema conditions by building the studio within a full-scaletheatre with monitoring, screen, rows of chairs, etc. and/or having adomestic set-up in another room. This allows the engineer toanalyse and judge the translation on the fly, thus freeing him/her to
focus on finalising all the details that make up a great end result.Although this approach deals with some of the translation issues inan effective way, it is not necessarily the best solution, if youconsider the investment involved.
Another route for dealing with the translation challenge is tosetup and optimise a monitoring system in a smaller room to givean approximation of several listening conditions. Most small roomsystems can be improved remarkably with little means but know-how and creativity, and turned into a reliable reference.
The following article will deal with ways to setup and optimise a5.1 reference monitoring system to provide flexible mastering ormixing facilities with accurate monitoring of audio in various formats.
DVD Mastering Audio in 5.1 FormatWith the growth of interest in surround sound encoding there hasbeen a great deal of confusion regarding the best way to set up amastering facility to accurately monitor the audio channels in agiven format.
With the advent of digital, discrete multi-channel recording all of
the limitations of matrixed 4:2:4 systems were removed at a stroke.Although DVD will be used for other formats it will still be heavilyinfluenced by the film industry (DTS and Dolby Digital). Havingsaid that I do recognise the potential in DVD for more linear audioformats which do present possibilities for much higher fidelity thanthe data-compressed formats, but that is another story all together.
DVD Mixing Studio vs. Film Dubbing TheatreThe essential question at the moment is how to set up the smallercontrol room environments used for DVD mixing compared to thetraditional film dubbing theatres which have been mixing 5.1 for
several years? To judge this it is important to recognise therelationship between the direct and reverberant sound ineach room. The person judging the sound balance andquality must hear the correct blend of direct energy fromeach speaker and a pre-determined amount of roomreflection and reverberant energy. The ratio between thetwo can be controlled by the following factors:
• speaker directivity over the required frequency range.• distance from the speaker to the listening position.• room volume and geometry.• room acoustic and absorption.By manipulating these factors that it possible to obtain a
balance in a smaller room of, say, 50 square metres, which issimilar to a much larger theatre with a highly directionalhorn – at least in the speech frequency band which is themost important from an intelligibility point of view.
If we compare the sound level produced by a horn-loaded speaker and a direct radiating driver in the same theatre atvarying distances from the screen; it can be seen that although thehorn produces a much higher sound level close to the speakers,when we measure at a larger distance the levels are almost thesame. This is because we are well into the reverberant sound fieldand the direct sound no longer has much influence, except that itarrives at the ear first and this is why we can still perceive somekind of stereo image, even when the sound is dominated by theroom itself. The distance from the speaker at which the direct (Ld)and reverberant (Lr) sound levels are equal is called the criticaldistance, Dc, and in a large theatre it is important to design theacoustics and the sound system so that all of the audience isbeyond the critical distance and yet still within the coverage angleof the speakers. Ignorance of this fact accounts for the largenumber of complaints received by cinema operators of the ‘tooloud’, ‘couldn’t understand what he was saying’ variety.
Beyond the critical distance the sound level is dominated by theroom energy and remains constant (apart from local effects causedby poor geometry and room resonance, of which more later).
70
5.1 Monitoring SetupYou don’t need a studio the size of your local multiplex to simulate a cinema experience. AndyMunro & Thomas Lund discuss ways to setup and optimise a 5.1 reference monitoring systemto make it as flexible and as accurate as possible.
To locate the critical distance, Dc, it can be shown thatDc = !QR/16"Q is the directivity of the speaker (1 being omni directional and 30 a
very narrow mid range horn).R is the room absorption which can be measured or designed
according to the required reverberation time.By reducing the speaker Q it is possible to arrive at the same direct-
to-reverberant ratio with both horns and wide dispersion nearfieldspeakers. We can compare our large dubbing theatre with its large hornspeaker with a smaller room using a smaller pair of soft domemonitors.
Most horn configurations will produce a negative ratio (i.e. the roomreverberation is the dominant factor) in most large dubbing theatres.Therefore monitors in small rooms need to be as un-directional aspossible, if it is desired to emulate a theatrical sound field.
This is particularly true in the reproduction of sound in 5.1 format.The object of the exercise is to recreate a realistic sound field based onwhat we perceive as natural. That means discrete, visually interactivesounds from the front channels and indirect or ambient sound from therear, with the occasional directional effect to give interest to the mix.
This is a far cry from some of the audio-only 5.1 mixes I have heard,which could cause severe neck ache, not to mention a low irritationthreshold once the novelty of the lead guitarist hanging on the backwall begins to wear off ! I am reminded of the early days of stereo LPs,when ping-ponging sounds and trains panning across the living room
were the order of the day.The most pleasing results will occur when the room (monitoring or
listening) is not too dead, and the speakers are very open and actuallygiven some space to radiate before early reflections contrive to destroythe spatial images of the mix.
I have noted that multi-channel digital sound has created a demandfor mixing theatres which are, if anything, more live that the equivalentold analogue rooms.
I can only explain this in terms of naturalness and adherence toaudio fidelity which I think bodes very well for the future.
71
Manufacturer: ATCSystem: Concept 4What You Get: 4 x T16 + 1 x T16 Centre + 1 x Active Sub.T16 Spec: Theon-board amplifi-cation provides atotal of 250W(200W + 50W) ofcontinuous powerand is matched tothe one-inchneodymiummagnet fabricdome tweeter and6.5-inch ATC soft-dome mid/bassdrive unit. A singlepiece, ‘rigorously’damped aluminium casing forms five sides of the speaker andincorporates a heat sink, carry handle and control/connectorpanel. The T16 Centre contains two mid/bass drivers and isdesigned for use with direct and projected TV as well as largescreen front projection.What The Marketeers Say: “The all new T16 is directlydescended from ATC’s highly successful Professional 20 andthe award winning SCM20 monitors. Thus exceptional stereoand multichannel performance is assured.”Price: $27,995Contact: Alistair Dewar at Technical Audio Group.Phone: (02) 9810 5300Email: [email protected]: ‘www.tag.com.au’
Manufacturer: KRKWhat You Get: 5 x V6 + 1 x S10 sub.V6 Spec: Thesemonitors featureactive crossover,bi-amplification,six-inch bassdrivers/one-inchsilk-dometweeter. Theirfrequencyresponse is aquoted 58Hz to22kHz.S10 Spec: Thissub uses a 10-inch kevlarwoofer, and thefrequencyresponse rolls offat 80Hz. The active crossover is configured for either LCR or5.1 installations.What The Marketeers Say: “The ‘main drawcards’ of thissystem is the incredible response of the V6s. Their mid range
The Contenders
30°
110°
The ITU-R 775 spec places the surround speakers 110° from the centrespeaker and the left/right speakers 30° from centre. all speakers areequidistanat from the listening position.
72
5.1 Speaker Set-upMany people are unsure about the best way to set out speakers forDVD mastering. The ITU-R 775 specification has been adopted bybroadcast engineers and it is now used in many critical listeningrooms. The front three speakers should be positioned equi-distantlyfrom the mix position with an angle of 60 degrees subtended by theleft and right. All three should be identical models with a matchedresponse within ±3dB in any third-octave band between 250Hz and2kHz, measured at the mix position. The limits can be slightly relaxedabove and below this range, but for mastering purposes this would notbe advisable.
The surround speakers should be positioned at the same distanceto the mix position as the main front speakers, at an angle of 110degrees from the centre line. If this is not possible then a digital delayshould be used to bring the speakers back into coincidence. Ideallythe surround units will be the same as the front ones, but if that is notpossible they should be of the same manufacturer using identicaldriver technology. The polarity and phase summing of each speakershould be such that any two together will produce an increase insound level of between 3dB and 6dB at any frequency up to 10kHz.Above that frequency it is difficult to place the microphone soprecisely that phase coincidence is perfect (but many purists will insiston trying).
Several differences to this set up must be considered in the contextof film sound:
• The larger rooms used for film mixing dictate that several pairs ofsurround speakers are used, to ensure that everyone in the room hearsthe same delay and direct to reverb ratio. The use of time delay andseparate power amplifiers is recommended to achieve consistentresults. THX maintain strict criteria for surround speaker placement inorder to achieve world wide compatibility between theatres anddubbing stages:
• The surround speakers must often be placed at high level andangled to cover a large area at constant level.
• The surround speakers are rarely the same as the front oneswhich are invariably large, horn loaded systems of considerable bulk.
• The angle subtended by the main left and right speakers shouldbe 45 degrees at the mixing console. This assumes the speakers are atthe extremes of the screen which begs the question, ‘how do weadjust for different film aspect ratios?’. One solution is to use fivespeakers at the front, the inner pair used for TV formats and the outerpair for wide screen ratios.
This final consideration apart, it should be possible to maintaincompatibility between the two formats, so long as good use is made oflow directivity speakers in small, dry rooms.
The LFE ChannelIn a true 5.1 system the .1 is a discrete low frequency channel whichis used by the mixing engineer to create special effects and to extendthe normal frequency range of music and other mixed events. Thechannel can also be used as a sub woofer system to accept a feed ofbass from the main speaker channels whose speakers may be toosmall or unsuitable to reproduce high levels of very low frequencymaterial. This mode is created in the decoder of the playback systemand is a user definable mode, not one which would normally be con-sidered in the mixing or mastering room except for comparative useor plain curiosity.
In data compressed formats, the LFE channel contains a steepfilter at 120Hz which prevents higher frequencies leaking into theLFE track. Dolby recommend an 80Hz filter in the console channels
and top end is bright, clear and easy to get used to. While theydo use a relatively small bass unit, the S10 fills this void withtight controlled subs, creating a great sounding surroundsystem.”Price: $8,500Contact: Brent Heber at Syncrotech System Designs.Phone: (02) 9879 0800Email: [email protected]: ‘www.krksys.com’
Manufacturer: YamahaSystem: MSP Surround monitor systems.What You Get: 5 x MSP5 + 1 x SW10 sub; or 5 x MSP10 +1 x SW10.MSP5 Spec: 12cm bass driver and 2.5cm titanium waveguidetweeter mated to a pair of 40W and 27W amplifiers, the MSP5is capable of producing 50Hz to 40kHz frequency responseand a maximum output SPL of 101dB.MSP10 Spec: Quoted frequency range from 40Hz to 40kHz.An eight-inch shielded bass driver and one-inch titaniumwaveguide tweeter are powered by a pair of 120W and 60Wamplifiers respectively. The MSP10 offers low and high EQswitches for tailoring of room response, and a built-in 80Hzhigh-pass crossover for bass management.SW10 Spec: This sub uses a long-stroke 10-inch driver matedto a 180W amplifier to extend the frequency response to ‘thelower limits of audibility’. The 25Hz to 150Hz frequencyresponse and multiple I/O connections make system wiringsimple, even in systems where bass management is notavailable.What The Marketeers Say: “With a choice of using allMPS10s, a mix of 10s and 5s, or all MSP5s along with a SW10subwoofer, the MSP range of speakers have been designed tosuit a variety of surround monitoring applications. Frommidfield dubbing stages down to the smallest OB vans, theMSP system components offer the ideal choice.”Price: $9,770 (MSP10/SW10 ); $5,270 (MSP5/SW10).Contact: Danny Bishop at Yamaha Music AustraliaPhone: (03) 9693 5184Email: [email protected]
The Contenders…
73
to make sure nothing is even heard (and therefore localised by thefinal audience).
The LFE channel speaker is set at a level 10dB higher than the otherchannels in the mixing theatre, so it is important to do the same in anyreplay situation. This should be done with band limited pink noise tosmooth out localised pressure wave variations.
Most music mixing engineers do not send material to the LFEchannel as there is enough mutual coupling of the main speakers toproduce more than enough low frequency energy. In fact, a wellmatched system will produce up to 10dB more bass than a singlespeaker and care must be taken to balance the mix accordingly. TheLFE channel would obviously be useful for extended effects such ascannons and organ pipes and music reproduced down to 20Hz or less,and will doubtlessly become more interesting as skills and productionvalues improve. We may even see an improvement in pop music mixesas engineers finally realise that small, closed box woofers (rolling off at70Hz) do the serious audiophile no favours at all.
More AcousticsSeveral people have asked me how to ensure that all five speakerssound the same, and the answer is basically down to a few key factors:
• The room must be symmetrical about the centre speaker axis, withwindows and doors placed so as to steer sound reflections away fromthe mix position.
• Early reflections (within 15ms of the direct sound) should have anamplitude of no more that 10dB below the direct sound, especially inany band between 250Hz and 2kHz.
• Each speaker should be placed at least one metre from any walland not equidistant to two walls (or they should be completely flushwith the wall for large soffit-mounting systems).
• The room acoustic should be as diffused as possible with a rever-beration time of [0.25(V/100)] ±0.05s. In other words the referencevalue is 0.25 seconds for a 100 cubic metre room, increasing with roomsize (where ‘V’ is the room’s volume). My favourite spaces are oftenabout this value so I would argue that the ISO/MPEG/SMPTE guyshave got it about right.
• Room proportions should not be vastly different, but never thesame, and cubic is a disaster. Room modes will always dominate thelow frequency performance, closely followed by first reflections fromfloor and ceiling. I’d say a 7m by 5m by 3m is a good starting point formastering rooms.
• Background noise should be judged according to material and thefinal medium. Film and pop music are often mixed in rooms with anoise floor of NR30, because a mix which is too wide in dynamic rangewill cause problems on playback (noisy theatres, car radios, walkman inthe street etc.). A critical listening room needs to be very quiet so as tojudge the limits of other systems’ dynamics, and NR10 to NR15 mightbe called for in some circumstances.
Final TakeDVD is a new and exciting medium with huge potential for extendingaudio quality beyond anything the average consumer has experiencedbefore. The industry is suffering greatly at the moment because indeci-sion and format wars are diluting the message. There have been toomany half-cocked proposals put about lately, so let’s just get on with itbefore gangrene sets in!
Check out ‘Setting Up A 5.1 Studio’ in AT Issue 11 for more of the basicsof multi-channel audio and putting together a 5.1 room.
Manufacturer: HaflerWhat You Get: 5 x TRM8 + 1 x TRM12 sub; or 5 x TRM5 +1 x TRM10 sub.TRM8 Spec: Bi-ampedactive design(75W/150W),balanced/unbalancedinputs, selectabletreble/bass shelving forachieving the requiredsound by the user.TRM6 Spec Bi-ampedactive design(33W/50W),balanced/unbalancedinputs, selectabletreble/bass shelving forachieving the requiredsound by the user.What The Marketeers Say: “The TRM8 active bi-ampedmonitors have been proclaimed by many studio engineersaround the world as being the finest nearfield monitorsavailable at any cost. The TRM8 incorporates Hafler’s propri-etary ‘trans.nova’ amplifier circuitry coupled with Hafler’s ownloudspeaker components. The result is a listening environ-ment that will please even the most discerning of studioengineer. The addition of the 12-inch active subwoofercompletes the perfect 5.1 monitoring system.”Price: $9,995 (TRM8/TRM12); $7,995 (TRM6/TRM10).Contact: Derek Croser at Network Entertainment Technology(formerly GUET).Phone: 0409 397 954Email: [email protected]: ‘www.hafler.com’
Manufacturer: JBL Professional System: LSR28P 5.1 or LSR25P 5.1 System.What You Get: 5 x LSR28P + 1 x LSR12P sub; or 5 xLSR25P + 1 x LSR12P sub.LSR28P Spec: The LSR28P is an eight-inch two-way bi-amplified nearfield monitor with 250W for LF and 120W forHF. Also included are a number of different dip switches forsetting response options as well as clip limiters for device pro-tection. Frequency response is quoted at 50Hz to 20kHz (+1, -1.5dB), with useable bass extension to 36Hz.LSR25P Description: The LSR25P is a 5.25-inch two-way
The Contenders…
AT
bi-amplified workstation monitor with 100W for LF and 50W for HFwith full magnetic shielding on both woofer and tweeter, allowinguse in close proximity to video display units. Also included are anumber of different dip switches for setting response options aswell as clip limiters for device protection.LSR12P Spec: The LSR12P is a 12-inch bass reflex subwooferwith a 250W power amplifier and integral bass management pro-cessing. A contact closure switch is provided for comparison formixed with and without bass management.What The Marketeers Say: “Using JBL’s Linear SpatialReference design philosophy, the monitors exhibit a very smoothand uniform response not only on axis but also within a very largearea off axis. The results being that the monitor system has a verylarge perceived sweet spot. Additionally, the LSR28P 5.1 System hasattained THX approval status.”Price: $16,995 (LSR28P System); $9545 (LSR25P System).Contact: Nick Orsatti at Jands Technical Resource Group.Phone: (02) 9582 0909Email: [email protected]: ‘www.jblpro.com’ or ‘www.jands.com.au’
Manufacturer: Dynaudio AcousticsSystem: Sys-tem 2S or Sys-tem 2M.What YouGet: System 2S– 5 x BM6A +1 x BX30A; orSystem 2M – 3x M1.5 + 2 xBM15A(surrounds) + 2x BX30A.BM6A Spec:The BM6A isan active two-way systemincorporating matched on-board amplification and system controlelectronics. Features include: dual 100W MOSFET amplifiers,adjustable LF & HF trims plus a slow-attack optical HF limiter. AllBM6A cabinets are matched to within 1.5dB of each other.M1.5 Spec: Suitable for either stand or soffit mounting, the totallypassive M1.5 relies on component quality for its performance. Thehigh sensitivity drivers were developed exclusively for this modeland coupled with a twin-ported cabinet plus an impedancecorrected crossover to ensure that optimum loading is presented tothe amplifier at all times. Quoted frequency response of 34Hz to20kHz and a maximum output in excess of 120dB SPL @ 1m.What The Marketeers Say:: “The BM6A has received wide-spread international acclaim for its unique linear phase andfrequency response, high output level and pinpoint imaging.Meanwhile, the M1.5 is renowned for its ability to deliver extraordi-narily high output levels from a comparitively compact cabinet andcan actually outperform many ‘main’ monitor systems. Imaging ispin sharp, even in difficult environments, thanks to the directionallycontrolled tweeters.”
Price: System 2S – $16,880; System 2M – $27,790.Contact: Chris Royal at Amber Technology.Phone: (02) 9452 8600Email: [email protected]: ‘www.ambertech.com.au’ or ‘www.dynaudioacoustics.dk’
Manufacturer: PMCWhat You Get: 5 x AML-1 + 1 x XB1-A; or 3 x AML-1 + 2 xTB2SM-P (surrounds) + 1 x XB1-A.AML-1 Spec: The AML-1employs a 165mm flat pistonbass driver which boasts aquoted sub-35Hz performance.A soft dome unit is used forhigh frequencies. The Brystonamp has bypassable usercontrols to provide for inputlevel adjustment, LF roll-off, LFtilt, and HF tilt.TB2 Spec: This two-waynearfield monitor has a quotedfrequency range of 40Hz to25kHz with a 170mm cast chassisbass driver and 25mm ferrofluidcooled alloy HF unit. In this casethe TB2 is powered by a Brystonmonoblock amplifier.XB-1 Spec: This sub uses atransmission line design withdie-cast 10-inch dual voicecoil woofer. Power handling is up to200W, and has quoted figures of 25Hz to 200Hz frequencyresponse and a sensitivity of 90dB SPL/W/m.What The Marketeers Say: “PMC implement their own uniqueversion of the transmission line principle, producing full-scale per-formance and incredible bass extension. The advantages of trans-mission line technology are: full frequency response at all listeninglevels; lower colouration; neutral and dynamic performance;accurate and extended LF performance; and higher power handlingwithout distortion or compression.”Price: $23,672.50 (AML-1/XB1-A), or $20,397.50 (AML-1/TB2SM-P/SB1-A).Contact: Don Dowling at Neotec Audio.Phone: (02) 9873 3994Email: [email protected]: ‘www.pmcloudspeakers.com’
Manufacturer: GenelecWhat You Get: 5 x 1029A + 1 x 1091A sub; or 5 x 1030A + 1 x1092A sub.1029A Spec: The 1029A is a bi-amplified nearfield monitor con-structed from cast aluminium, and features magnetic shielding. A6.5-inch polymer composite driver and a 0.75-inch metal dometweeter are used. It has a quoted frequency response of 52Hz to20kHz and a peak performance of 115dB SPL per pair @ 1m withmusic material.1091A Spec: This sub incorporates the amp and all crossoverelectronics needed to combine it with the 1029A loudspeakers. It
The Contenders…
74
reproducesfrequencies of38Hz to 85Hz(±2.5dB), anduses a24dB/octavecrossover.One front-loaded eight-inch conedriver is usedin a 15 litrecabinet. Theamp produces 70W of output power, and has circuit protection.1030A Spec: The 1030A uses a 6.5-inch polymer composite conedriver and a 0.75-inch metal dome tweeter loaded with Genelec’sDCW (see below). It’s a 6.5 litre cabinet, bi-amplified (80W/50W),has a quoted sensitivity of 115dB SPL (peak) per pair @ 1m withmusic material, and a quoted frequency response of 52Hz to 20kHz (-3dB). The unit also packs built-in bass rolloff, treble and basstilt controls.1092A Spec:The 1092A uses two eight-inch cone drivers housedin a 55 litre vented cabinet and are front loaded. The amplifierproduces 180W of short term RMS power and includes circuitry fordriver overload and thermal overload protection.What The Marketeers Say: “Genelec’s unique DirectivityControl Waveguide (DCW) is used for excellent stereo imaging andfrequency balance, even in difficult acoustic environments. Perfor-mance is comparable to much larger systems. The versatile roomresponse controls allow matching of the system to its surround-ings.”Price: $6,800 (1029A/1091A); $14,800 (1030A/1092A).Contact: David Sloss at Studio Connections.Phone: (03) 9874 7222Email: [email protected]: ‘www.genelec.com’
Manufacturer: Event ElectronicsWhat You Get: 5 x PS8 + 1 x20/20/15 sub or 5 x PS6 + 1 x20/20/12.PS8 &PS6 Specs: Thesemonitors use a magneticallyshielded eight-inch/6.5-inchmineral-filled polypropylenecone, and a similarly shieldedone-inch silk dome tweeter. ThePS8 has a quoted frequencyresponse of 35Hz to 20kHz(±3dB) while the PS6s extenddown to 45Hz. Both modelshave 200W of power on offer(130W/70W). A smaller 5/25-inch PS5 model is also in therange.20/20/15 Spec: This sub usesa 15-inch coated cone with foamsurround. There’s a quotedfrequency response of 28Hz to
120Hz (-3dB), and 250W power amp on board offering a maximumof 117dB peak @ 1 metre. A bass management system provides sixdiscrete, active balanced inputs, each with pass-through. The20/20/12 is a 12-inch version of this sub and has identical features,while the specs obviously differ somewhat given the smaller driver.What The Marketeers Say: “The PS8 and PS6 use Event’sspecifically designed active asymmetrical fourth-order crossover, withphase reponse so accurate that the resulting stereo imaging simplymust be heard to be believed. Meanwhile the 20/20/15’s massive 15-inch driver delivers thundering low end with incredible detail andclarity.”Price: $8,996.50 (PS6s + 20/20/12) or $10,996.50 (PS8s + 20/20/15).Contact: Ian Flowers at Music LinkPhone: (03) 9765 6565Email: [email protected]: ‘www.event1.com’
Manufacturer: ITC(Landmark)What You Get: 5 x LM1-B + 1 x LSX sub.LM1-B Specs: The LM1-B is a passive design. Thequoted specs measure thefrequency response 3dBdown at 55Hz and 20kHz,a sensitivity of89dB/w/m, and amaximum continuous SPL@ 1 metre of 98dB. TheHF and LF units crossover at 1750Hz.
What The MarketeersSay: “The Landmarkrange of speakers are Australian owned and made. In fact, most ofthe final ‘mother’ mastering for CD production that is performed inSydney is now done on Landmark LM1-B and Landmark LSXmonitors. ITC’sapproach is to select theappropriate monitorconfiguration for theclient and then optimiseeach loudspeaker for theroom it is feeding. Thephase of the tweeter ispassively adjustedduring manufacture (foreach client), thusensuring that the systemis in phase at crossover(normally impossible ina passive design).”Price: $5,397.50Contact: Gerald StewartPhone: (02) 9482 1286Email: [email protected]
76
The Landmark LSX Sub with optionalLM2 centre speaker.
