28 CREATION
April 2016
Where clipping really occurs
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Since 2012 , the audio-engineering departments of many TV broadcasters have gradually switched from QPPM metering to loudness normalisation , a new unit for level : TruePeak ( dBTP ) and standards that are based on ITU-1770 .
The approach with TruePeak metering is particularly important for applications operating right below the technical clipping level ( for example , in CD mastering ) in order to prevent overloading D / A converters of CD , MP3 , or other players .
As you just cannot achieve a higher level than with all bits set , the full-scale ( FS ) level cannot be exceeded . Twenty-four-bit provides more dynamic range than
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When it comes to metering and headroom configuration in DAWs ( digital audio workstation ), things can really get complicated , as RTW ’ s Michael Kahsnitz explains .
16-bit ; this is because the analogue signal is represented by one from a total of 224 discrete values ( compared to 216 values ). Expressed in dB , this means that the theoretical signal-to-noise ratio of an n-bit system is appropriately n × 6.02 + 1.76dB . ( For example , for 16-bit , this is 98dB ; for 24-bit , it is 146dB .)
Now if you look at the overall dynamic range of a 24-bit signal at a level of 146dB , setting the operating level to -24 dBFS ( -24 LKFS / 0
LU ) is almost perfect . There is sufficient headroom and the gap to the noise floor is large enough too .
Digital audio consists of equally long slices or samples , with their numerical values each representing actual signal voltages . At a sample rate of 44.1kHz , a new value is sampled every 22.68 µ s . Between any two samples , however , an analogue signal can achieve an infinite number of possible signal voltages at lengths inclining towards infinitely
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short . The shorter the signal , the higher the frequency ( f = 1 / t ).
Digital audio typically has a finite level . This means that signals exceeding the full-scale level are just truncated , resulting in undesirable distortion . True-peak metering was introduced to avoid this . With true peak , the signal is sampled with at least four times the nominal sample rate — in our case , every 5.5 µ s . As this still does not ensure safe recording , an upper limit of -1 dBTP was additionally specified .
Metering in the DAW
Almost all DAWs ( digital audio workstations ) use floating-point arithmetic ; simply put , this creates
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an almost unlimited range of values . In DAWs , the meters often show clipping that is neither audible nor visible in a vectorscope .
This means that DAW meters are far from being reliable for absolute output level reading , and using a vectorscope for clipping checks is unsuitable . Things are different when using an external programme for metering and generating vectorscopes from the output signal : As such a programme applies the finite 24-bit range , it will show all artifacts any converter would produce while playing the signal .
Michael Kahsnitz is Head of Product Management for RTW .
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Amira takes a bite of China
A Bite of China : Celebrating the Chinese New Year is a documentary feature film released to celebrate the recent 2016 Chinese New Year . Travelling all over China , the crew shot more than 10,000 minutes of footage at 24 locations , documenting 43 regional dishes .
ARRI ’ s Amira was chosen as the film ’ s A-camera , as Chen Lei , the film ’ s director , explained : “ At the pre-production stage , it was very clear to us that choosing the right equipment would be crucial . Shooting for cinema requires a high-quality cinema and naturally , ARRI cameras were our first choice .
“ Many of the cinematographers on our team … spoke highly of ARRI cameras in terms of image quality , colour rendition and reliability . In the end , we settled on the Amira , as it was primarily designed for documentary-style shooting .”
Chen added that what most impressed him about ARRI cameras is the “ excellent colour rendition ”, with the Amira able to bring out the texture and colour of food in the film . “ In addition , I was also impressed by the dynamic range and high sensitivity . A couple of spontaneous moments in the film were not lit properly due to time constraints but the results turned out surprisingly well . Amira still managed to capture rich details in low light conditions — it helped us tremendously ,” he said .
Cinematographer Zhao Li Wei pointed out a specific scene where a girl was filmed preparing some freshwater snails by a well . The scene was backlit by the sun and there was a huge tree casting shadows on the girl , while the water was reflecting the sunlight , resulting in a high contrast between subject and background .
Zhao explained : “ To ensure the best image quality in a theatrical environment , we were very conservative with the exposure and the director was concerned about shadow details , but in the end , the footage we captured had excellent tonal range . The [ Amira ] camera performed so well that it put our minds at ease for the rest of the shoot .”
Additionally , Amira ’ s highspeed ability proved to be a real asset , as many cooking scenes happened fast and the crew had to use slow motion to capture the details . “ Shots of ingredients falling into
ARRI ’ s Amira was chosen as the A-camera for the filming of Chinese documentary feature film A Bite of China : Celebrating the Chinese New Year .
water or pots tended to look much better in slow motion . Amira was able to shoot 200fps at full sensor resolution without any quality loss , which was exactly what we needed ,” Zhao concluded .
New Al Kass OB van outfitted with Lawo equipment
Delivered in January this year , Qatar sports channel Al-Kass ’ new OB-10 , 31-camera truck is making extensive use of Lawo equipment to serve the sports channel ’ s coverage of some of the largest events in the region .
Central to the audio set-up is a 48-fader Lawo mc ² 56 audio mixer fitted with local I / Os and 384 DSP channels , allowing OB-10 to handle the most demanding productions . Its connectivity includes 96 AES inputs / outputs and two Dallis modular stageboxes , which provide 48 mic inputs and 16 line outputs each , alongside Riedel Artist intercom interfaces .
Three Lawo V __ pro8 8-channel video processing units provide the video tools necessary to support a variety of different video formats , as well as bridge between audio and video . High-quality format
The new Al-Kass OB-10 truck is widely outfitted with Lawo equipment .
conversion , colour correction and audio embedding / de-embedding make the V __ pro8 a “ powerful tool ” for the use of different standards and formats as part of an integrated broadcast set-up .
The V __ pro8 ’ s Dolby E encoding / decoding option provides up to four Dolby E encoders / decoders for fully compatible encoding / decoding of multi-channel audio , complete with Dolby metadata handling . In combination with the unit ’ s Dolby E Audio Aligner , the V __ pro8 provides a transmission path gateway for multi-channel productions .
Working as the overall control system in the OB-10 , Lawo ’ s VSM Broadcast Control & Monitoring system offers workflow flexibility and faster operational preparation . VSM is an IP-based control system and interfaces to all common hardware on the market , and has access to all relevant equipment within OB-10 .
As a hardware-independent control system , VSM connects to third-party manufactured equipment using proprietary protocols , as well as open standards . Using this combination , VSM controls the crosspoints within the truck ’ s Grass Valley NVision router and Nevion Sublime video router , with access to crosspoints , tally and labelling of the Grass Valley multi-switcher .
Interoperability with the audio equipment is also secured , with VSM having direct access to the crosspoints of the Lawo Nova audio router , as well as direct parameter control .
Running on redundant servers with Master-Master logic , the system provides “ maximum reliability ” and fail-safety , as well as links to the video and audio routers via redundant connections .