Loudness Meters: Absolute/Relative Scales …

Professional audio Loudness Meters measure Program (Integrated) Loudness using an Absolute scale displayed in LUFS (or LKFS). For example the EBU R128 Program Loudness target is -23.0 LUFS (Loudness Units Relative to Full Scale).

When the ITU defined new audio loudness measurement guidelines, the general consensus was that many audio engineers would prefer to mix to the familiar “0” level on a Loudness Meter for compliance targeting. A Relative scale option was implemented. It references Loudness Units (LU), where 0 LU equals the corresponding LUFS/LKFS compliance target.

So for EBU R128 … 0 LU == -23.0 LUFS.

In the snapshot below you can see my Nugen VisLM Loudness Meter set to display Absolute scale (left) and Relative scale (right).

scale-blog

Of course in most cases the scales and corresponding targets are customizable. For example I advocate -16.0 LUFS as the loudness target for audio distributed on the internet. By defining -16.0 LUFS as my Absolute scale compliance target in a meter’s setup options, 0 LU (Relative scale) would be equivalent to -16.0 LUFS.

Below is a basic side by side comparison of EBU R128 Absolute and Relative scales:

figg-scale

-paul.

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Internet Audio: True Peak Compliance …

Wide variations in average (Program/Integrated) Loudness are common across all forms of audio distributed on the internet. This includes audio Podcasts, Videocasts, and Streaming Media. This is due to the total lack of any standardized guidelines in the space. Need proof? Head over to Twit.tv and listen to a few minutes of any one of their programs. Use headphones, and set your playback volume to a comfortable level.

Now head over to PodcastAnswerMan.com, and without making any change to your playback volume – listen to the latest program.

I rest my case.

In fact, there is a 10 LU difference in average loudness between the two. Twit.tv programs check in at approximately -22 LUFS. PodcastAnswerMan checks in at approximately -12 LUFS. I find this astonishing, but I am not surprised. I’m not signaling them out for any lack of quality issues or anything like that. In my view both networks do a great job, and my guess is they have sizable audiences. Both shows are well produced and it simply makes sense to compare them in this case study.

With all this in mind let me stress that at this particular time I am not going to focus on discussing Program Loudness variations or any potential suggested standard. I can assure you this is coming! I will say that I advocate -16.0 LUFS (Program/Integrated Loudness) for all media formats distributed on the internet. Stay tuned for more on this. For now I would like to discuss True Peak compliance that will be a vital part of any recommended distribution standard.

What surprises me more than Program Loudness inconsistency is just how many producers are pushing files with clipped, distorted audio. In many cases Intersample Peaks are present in audio files that have been normalized to 0 dBFS. (For more information on Intersample Peaks please refer to this brief explanation). Producers need to correct this problem before their audio is distributed.

The Tools

One of the most useful features included in Adobe Audition is the Match Volume Processor. This tool includes various options that allow the operator to “dial in” specific average loudness and peak amplitude targets. After processing, the operator can examine the results by using Audition’s Amplitude Statistics analysis to check for accuracy.

mvp-1

Notice in the snapshot above I set the processor to Match To: Total RMS, with a -18.50 dB RMS average target. I’ve also selected the Use Limiting option. I’m able to dial in custom Look-Ahead and Release Time parameters as I see fit. Is there something missing? Indeed there is. Any time you push average levels you run the risk of clipping the source. In Audition the Match Volume/Use Limiting option lacks the capability for the operator to set a specific Peak Amplitude Ceiling. I’ve determined that in certain situations Peak Amplitudes reach a -0.1 dB ceiling resulting in possible clipped samples and True Peak levels that exceeded 0dBFS. Keep in mind this is not always the case. The results depend on the Dynamic Range and available Headroom of any source.

So how do we handle it?

Notice above the Match Volume Processor offers two Peak Amplitude options: Peak Amplitude and True Peak Amplitude. The European Broadcasting Union’s EBU R128 spec. dictates -1.0 dBTP (True Peak) as the ultimate ceiling to meet compliance. Here in the states ATSC A/85 dictates -2.0 dBTP. Since most, if not all audio formats distributed on the internet are delivered in lossy formats, it is important to pay close attention to True Peak Amplitude for both source (lossless) and distribution (lossy) files.

fgm

I advocate -1.0 dBTP as the standard for internet based audio file delivery. True Peak Limiters are able to detect and alleviate the possibility of Intersample Peaks from occurring. It is recommended to pass audio through a True Peak compliant limiter after loudness normalization and prior to lossy encoding. Options include ISL by Nugen Audio, Elixir by Flux, and (the best kept secret out there) TB Barricade by ToneBoosters. If you are running Audition, Match To: True Peak Amplitude and you should be all set.

The plugin developers mentioned above as well as Waves, MeterPlugs, tc electronic, Grimm Audio, and iZotope supply Loudness Meters and toolsets that display all aspects of loudness specifications including True Peak alerts. Visit this page for a list of supported Loudness Meters.

If True Peak detection and compliance is not within your reach due to the lack of capable tools, a slightly more aggressive ceiling (-1.5 dBFS) is recommended for Peak Normalization. The additional .5 dB acts as a sort of safety net, insuring maximum peak amplitude remains at or below -1.0 dBFS. One thing to keep in mind … performing Peak Amplitude Normalization after Loudness Normalization may very well result in a reduction in average, program loudness. Once again changes to the processed audio will depend on the audio attributes prior to Peak Normalizing.

Below I’ve supplied data that supports what I noted above. The table displays three iterations of a test file: Input, Loudness Normalized Intermediate, and final Output. For this test I used the ITU-R BS.1770-2 “Match To” option in Audition’s Match Volume Processor. I pushed the average target to -16.0 LUFS. As noted, this is the target that I advocate for internet and/or mobile audio. This target is +7 LU hotter than R128 and +8 LU hotter than ATSC A/85.

After processing the Input file, the average target was met in the Intermediate file, but True Peak overs occurred. The Intermediate file was then passed through a compliant True Peak Limiter with it’s ceiling set to -1.0 dBTP. Compliance was met in the Output with a minimal reduction in Program Loudness.

data-480

Producers: there is absolutely no excuse if your audio contains distortion due to clipping! At the very least you should Peak Normalize to -1.5 dBFS prior to encoding your lossy MP3. Every audio application on the planet offers the option to Peak Normalize, including GarageBand and Audacity. Best case scenario is to adopt True Peak compliance and learn how to use the tools that are necessary to get it done. If you are an experienced producer or professional, and you come across content that does not comply – reach out and offer guidance.

-paul.

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LoudMax and Final Cut Pro X

One of the great features of Final Cut Pro X is the availability of Apple’s 64bit Logic audio processing plugins (aka Filters). In fact FCPX supports all 64bit Audio Units developed by third parties.

Let me first point out I’ve tested a fair amount of 64bit Audio Units in FCPX. Results have been mixed. Some work flawlessly. A few result in sluggish performance. Others totally crash the application. I can report that Nugen’s ISL True-Peak Limiter and Wave Arts Final Plug work very well in the FCPX environment.

ISL is a Broadcast Compliant True-Peak Limiter that uses standardized ITU-R B.S 1770 algorithms. Settings include Input Gain and True-Peak Limit. ISL fully supports Inter-Sample Peak detection.

Final Plug allows the operator to set a limiting Threshold as well as a Peak Ceiling. Decreasing the Threshold will result in an increase of average loudness without the audio output ever exceeding the Ceiling.

Recently Flux released a 64bit version of Elixir, their ITU/EBU compliant True-Peak Peak Limiter. Currently (at least on my MacPro) the plugin is not usable. Applying Elixir to a clip located in the FCPX storyline causes an immediate crash. I’ve reported this to the developer and have yet to hear back from them.

The plugins noted above range in price from $149 to $249.

One recommendation that often appears on discussion forums and blogs is the use of the Logic AU Peak Limiter to boost audio loudness while maintaining brick-wall limiting. This process is especially important when a distribution outlet or broadcast facility defines a specific submission target. A few audio pro’s have taken this a step further and recommended the use of the Logic Compressor instead of the Peak Limiter. In my view both are good. However proper setup can be daunting, especially for the novice user.

These days picture editors need to know how to color correct, create effects, and handle various aspects of audio processing. If you are looking for a straight forward audio tool that will brick-wall limit and (if necessary) maximize loudness, I think I found a viable solution.

lM.jpg LoudMax is an easy to use Peak Limiter and Loudness Maximizer. Operators can use this plugin to drive audio levels and to set a brick-wall Output Ceiling.

The LoudMax Output Slider sets the output Ceiling. So if you are operating in the “just to be safe mode”, or if you need to limit output based on a target spec., set this accordingly. If you need to increase the average loudness of a clip – decrease the Threshold setting until you reach the desired level. The Output Ceiling will remain intact.

LoudMax also includes a useful Gain Reduction Meter. If viewing this meter is not important to you – there’s no need to run the plugin GUI. The Threshold and Output parameters are available as sliders, much the same as any other FCPX Filter or Template. You can also set parameter Keyframes and save slider settings as Presets.

lM-H

Using the Logic Peak Limiter and/or Compressor is definitely a viable option. Keep in mind that achieving acceptable results takes practice. Proper usage does require a bit more ingenuity due to the complexity of the settings. I’ll be addressing the concepts of audio dynamics Compression in the future. For now I urge you to take a look at LoudMax. It’s 32/64bit and available in both VST and AU formats. The AU Version works fine in FCPX. I found the processed audio results to be perfectly acceptable.

At the time of this writing LoudMax is available as Freeware.

-paul.

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Intersample Peaks, Normalization, and Limiting …

When preparing to encode MP3 files we need to be aware of the possibility of Intersample Peaks (ISP) that may be introduced in the output, especially when targeting low bit rates. This results from the filtering present in lossy encoding. We alleviate this risk by leaving at least 1 dB of headroom below 0dBFS.

Producers should peak normalize source files slated for MP3 encoding to nothing higher than -1.0 dBFS. In fact I may suggest lowering your ceiling further to -1.5 dBFS sometime in the future. Let me stress that I’m referring to Peak Normalization and not Loudness Normalization. Peak Normalizing to a specific level will limit audio peaks when and if the signal reaches a user defined ceiling. It is possible to set a digital ceiling when performing Loudness Normalization as well. This is a topic for a future blog post.

Notice the ISP in this image lifted from an MP3 wave form. The original source file was peak normalized to -0.1 dBFS and exhibited no signs of clipping.

You can also avoid ISP’s by using a compliant ITU Limiter and setting the ceiling accordingly. During source file encoding this type of limiter will detect when ISP’s may occur in the encoded MP3.

For podcast and internet audio, a limiter set to a standardized ceiling of -1.0/-1.5 dBFS works well and is recommended.

-paul.

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ProRes Proxy …

It’s been two weeks since I installed Final Cut Studio (3).

I spend most of my time working in Soundtrack Pro 3, and I’m happy with the new features. Most notably, RMS Normalization, Voice Level Matching, the “Enhanced” File Editor”, and a few additional editing features within Multitrack Projects (trim in point to playhead/trim out point to playhead, for example).

Final Cut Pro: I’m happy that apple finally added a customizable Timecode HUD, improved clip Speed Controls, and enhanced the process of Exporting work. Upon release of the suite the professional user base was up in arms with regard to the absence of dedicated support for Blu-ray authoring in DVD Studio Pro. However there is now a nifty (but limited) Blu-ray export option available from within Final Cut. Authoring templates are fairly basic, and of course a supported Blu-ray drive is necessary. So far this new feature has been well received. Incidentally, I heard from a reliable source that apple’s FC Studio Product Manager stated that “DVD Studio Pro is designed to author standard definition DVD’s.” Does this mean we will never see embedded Blu-ray support in DVDSP? Time will tell.

prores_prores_icon20090722.jpg

And let’s not forget about the new additions to the ProRes Family of codecs. In fact the Proxy and LT versions of ProRes will help with my AVCHD projects and workflows in a big way. It is now possible to ingest and edit transcoded camera footage using the reduced data rate ProRes Proxy codec.

I’ve been importing the contents of entire disc images that include the native AVCHD footage from my camera’s SDHC card and storing locally on a high capacity internal hard drive. This allows me to easily Log and Transfer multiple ProRes formats for editing, and for high quality ProRes (422 or HQ) reconnects in preparation for final output. I’ve been duplicating project edit sequences and adjusting settings accordingly prior to reconnecting to higher quality clips. This method works very well.

As far a disappointments: I was sure that apple would implement a major Final Cut UI overhaul for version 7. This was obviously not the case. Apple’s Product Manager also noted, and again according to sources – that the FC Pro UI “just works”, and there is “no reason to change it at this particular time …”

Anyway, as I move forward I will be spending more time working in and experimenting with Motion. I feel my Final Cut and Soundtrack Pro skills are where they need to be. Not the case with Motion.

Notes:

I’m now running the latest version of Final Cut Server (ver.1.5) and I have ordered a copy of Logic Express 9. I’ll be in touch…

-ptfigg.

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Audioarts Air 1 Console …

air_1.jpgAudioarts Engineering, a division of Wheatstone Broadcasting recently debuted their attractive small footprint Air 1 professional audio broadcast/production console. The company states the Air 1 was “specifically designed to meet the needs of on-air, production, news applications, remotes, and the emerging podcasting market.” Features include Dual program Buses, Cueing support, Long Throw Faders, Switchable PGM meters, 2 Monitor Outs, 2 Mic Preamps, Headphone Amp, Solid State Illumination on all switches along with a useful On-Air Indicator light.

Additional features include balanced 1/4″ I/O, external power supply for cool – hum free operation, and bottom mounted Dipswitches designed for easy programing. Lastly, the mic inputs can be programmed to automatically MUTE the Monitor Output when activated. The Air 1 is 2.5″ high, 15.25″ wide, 11.5″ front to back.

No doubt this is a slick device. My guess is professional fans of the Audioarts product line will find this console very attractive. It’s perfect for small scale operations and remote productions. However due to its $1800 price tag, I don’t anticipate wide adaptation within the new media/podcasting space. Standard, sub $1K audio mixers seem to be satisfying the needs of *most* new media producers.

-paul.

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