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Home | Library | Articles | A VU On Downmixing - Free Report

A VU On Downmixing - Free Report

by Shawn Micheal - V.P. Product Development
When Shawn isn't directing manufacturing, he's busy making the world a safer place for mixers.

Article summary: A free Report looks at the pitfalls and challenges of downmixing.

Featured in Audio Horizons Spring 2000 PDF 825k | Newsletter List
VuMAX product information

Martinsound is offering a new free Report. A VU On Downmixing will address engineers' concerns and promote discussion about surround sound format compatibility and downmixing.

With MultiMAX in use in many TV and post facilities around the world, Martinsound has a unique opportunity to not only watch but to participate in helping a fledgling format grow to maturity. As DTV, HDTV and DVD usher in a new era of compatibility checking for audio engineers, the days of simply mixing in mono or, more recently, mixing in stereo with a quick check in mono, are gone. Today, engineers mixing in 5.1 must check compatibility with a wide variety of formats.

Consumers can choose to listen to a mix in its original 5.1 format or rendered as 5.0, Dolby Surround™, LRS, LCR, Dolby Stereo™, Stereo or Mono, leaving little room for relational and phase mistakes. Additionally, consumers may select multilingual formats. For just one program there could be a large number of mix variations. And the bottom line is that live television precludes the opportunity of a second chance.

Though all the formats and downmixes must relate well to one another they can be very different. Dolby Digital™ 5.1 has full bandwidth stereo surrounds and a low frequency effects channel (LFE), Dolby Surround/Pro Logic™ does not. Great care must be taken when mixing to ensure that essential low frequency information does not appear exclusively in the surround or LFE channels, to guarantee compatibility with Dolby Surround and other formats. And consequently, the mixer must compare a Dolby Surround version with his original 5.1 mix, at reference SPL, to ensure their correlation.

Do not forget Dolby Stereo, an accepted broadcast format for many years due to its use on most movie soundtracks and stereo VHS releases, and the necessary delivery format for the millions of Pro Logic/Surround decoders worldwide. Dolby Stereo does not always provide satisfactory headphone reproduction and also does not maintain stereo surround information. Dolby Digital therefore allows consumers to choose to downmix a 5.1 mix to standard Stereo, but as with the downmix to Dolby Surround/Stereo, the caveat once again is that LFE will be lost.

Dolby Stereo and standard Stereo downmixes are very different, but in spite of those differences mixers not only expect to make a direct comparison between Dolby Stereo and standard Stereo downmixes but also expect to compare the mono counterparts of these two very different downmixes.

This begs several serious questions that involve both equipment headroom and audio perceptions. Should these mixes and downmixes be monitored at the same SPL? When switching from a 5.1 monitor system to a single mono loudspeaker, should the overall SPL remain the same or should it vary as the quantity of speakers varies? Is a total SPL of 90 dB from five different directions and LFE perceived the same as 90 dB from only one direction?

We are offering information and promoting further discussion with two free Reports, A VU On Downmixing and Secrets Of Doing Surround Sound On Your Existing Console. Through these Reports you will not only become aware of the pitfalls that lie ahead but also the straightforward surround monitoring solutions that Martinsound has available through products such as MultiMAX and ForMAX.


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