This page contains a Flash digital edition of a book.
March 2014 www.tvbeurope.com


TVBEurope 19 Loudness Forum Plunkett: The loudness


measurement on a down-mixed stereo audio can be significantly different than that measured on the discrete surround version, especially where there is a great deal of correlation between the channels as they are summed together. It is therefore important to check the loudness post down-mix and for sound supervisors to understand the possible consequences. Schut: There shouldn’t be other than that some video formats require different levels. van Everdingen: There can be loudness differences between multichannel audio and the down-mix. This is also affected by down-mix parameters such as the Centre and Surround down-mix levels. In practice, the down-mix level will fluctuate a bit if the


“I found in my own research Steve Plunkett, Red Bee Media


is tricky. Currently, the PLOUD group is doing research to ascertain if the LRA measurement can be slightly optimised so that some specific mixes that have a high LRA number correlate better with the human perception. Even if it comes to an improved LRA measurement, extensive testing is required in my opinion before it is recommendable to use a certain number as a restriction, especially if this number is chosen relatively low.


Are there special considerations when down- mixing from Surround to Stereo using the Loudness standard?


Camerer: Unfortunately, it is not possible to predict the loudness of a down-mix from surround sound to stereo, judging only from the downmix parameters. This is due to the


different influence of the level of the surround channels, as well as the use of divergence — ‘bleed’ — of Centre signal into left and right. The more surround-heavy content you have — applause, for example — the bigger the loudness difference of a stereo downmix will be. There is no single solution to that. Best practice is to transmit two separate mixes, both loudness normalised — and not to rely on an automatic downmix at the consumer’s end. Carroll: Downmixes can cause slight loudness variations which are completely programme dependent. This is why some of the regulations enacted throughout the world have a tolerance of +/- 1 to 2dB. Having zero tolerance may result in additional — and unnecessary — processing whose only goal is to satisfy a meter. This needs to be watched carefully as heavier processing is an easier and less expensive answer for compliance versus remixing but can often lower quality.


What is the next development on the Loudness issue?


Burrows: We are not currently planning any changes to the UK DPP Loudness specifications published last year, but we will monitor progress and if through experience we identify any areas requiring optimisation, we will consider making minor adjustments to the spec. In the meantime we will continue with our industry training and collaboration initiatives. Camerer: Loudness


that excellent mixes with good speech intelligibility and a


consistent voice level close to programme


loudness can have very high LRA figures, up


to 22, without causing a problem”


Richard van Everdingen, audio consultant


multichannel programmes are loudness normalised. The broadcast station can check content in the ingest stage to prevent tricks being applied that make the down-mix unreasonably louder, for example in commercials. There is, however, also another way to work around the issue. In the Netherlands, the main stations use simulcast audio on cable networks. There is a dedicated stereo service and a separate service for multichannel audio. Dependent on the playback configuration, the viewer can choose the stereo or the surround service on IDTVs and set-top boxes. This offers the possibility to optimise both, independent from down-mix and up-mix issues.


normalisation in radio is the logical next step. There are a few differences and many things in common with TV. Once loudness normalisation is established in radio, it will have a strong impact on music production too, together with streaming services becoming more and more loudness normalised, for example, iTunes Radio. Carroll: I


believe this issue of tolerance has to be handled before


processing is increased just to hit a meter-


satisfying result. Nicholas: I would predict


that the next development in the loudness issues would be that all developers and vendors agree on the method to convey clear indications of whether a piece of audio content has been measured to a known standard and whether it was compliant. If processing has been applied that should also be indicated. This indicator should be able to be read by all consumer devices to prevent ruinous multiple loudness corrections being applied to a piece of content. It would be advantageous if such a process were also able to handle the advent of object-based audio that is now getting a lot of attention within our industry. Pascoe: The EBU PLOUD


group now have other platforms firmly on their radar; radio and cinema being amongst them. While the technical solutions for measurement are


now in place, lack of industry consensus is most likely to be a barrier to adoption. Plunkett: If we do a good job


of introducing R128, the next development should be that loudness disappears as an industry and viewer concern. Let’s hope that we can do so. Schut: I would expect some


improvements in automated correction algorithms from different vendors. Implementing improved metadata where signals that are correct are left alone and not affected by downstream loudness controllers as proposed by Dolby. And I hope for better understanding of the problem where there is the most control — in production. van Everdingen: The group is spending time on implementation issues and is also working on radio at the moment, particularly the alignment between DAB and FM radio. www.orf.at www.axon.tv www.channel4.com www.cobaltdigital.com www.delta-sigma-consultancy.nl www.digitalproductionpartnership. co.uk www.dolby.com www.linearacoustic.com www.redbeemedia.com www.tech.ebu.ch/groups/ploud


Tim Carroll, The Telos Alliance/Linear Acoustic


Mark Pascoe, Dolby Laboratories


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52