FAQ for Audio Post Production QC
Updated by Rick Recco on 3/7/2024
Here is a list of Audio Quality Control Questions we frequently get asked about QC of Film & Movie Video/Audio, and The Broadcast Industry. This FAQ for Audio Post Production QC will answer those questions. This page combines Audio FAQ questions. It is also broken down by category in the links above.
Q: How is audio measured? What are the correct audio specs for a stereo or M&E mix?
A: Audio levels are measured using audio meters and phase scopes. Levels are measured on a scale known as dbfs. The dbfs scale is measured as negative numbers, with zero being the highest allowable level in movies and films.
Audio begins to become audible at -90dbfs. The reference tone for audio levels in the United States is set at -20dbfs. This is the level that the tones, in the bars & tones should be set to. This is used to ensure that all audio is measured the same. At the reference level of -20dbfs, audio levels will be average for a normal conversation that you would hear on a show. (Tones will match average program audio levels.) Many Television networks limit audio to peaks at -12 or -10 dbfs, For movies 0 dbfs is the Audio peak limit. Any audio that goes above 0 dbfs is considered “clipped” and will usually cause distortion. A Quality Control report will list the audio peaks and any instances where the peaks are clipped.
Q: Our film received a rejection for excessive Loudness. What is the difference between Audio Loudness and Audio Peaks?
A: There are several measurements we take when doing the audio portion of a Film or TV QC Report. “Loudness” refers to the overall average of the dialogue throughout the entire show. Metering loudness is a fairly recent addition to QC. Measuring Loudness came as a result of a law called the “Calm Act.” This law is to ensure audio levels are the same across all TV shows, movies and commercials. Have you ever been watching a show, and a commercial comes on that is much louder? This is what the calm act tries to stop.
Audio Loudness differs from audio peaks, which are the highest levels the audio reaches during the program. Loudness levels have mostly replaced audio averages on QC reports as they are more specific, and measured differently. Loudness is measured on a scale known as LKFS, or LUFS. Under the Calm Act a Loudness reading should be between -22 & -26 LKFS / LUFS. These levels are measured using specific programs that measure Loudness, such as Adobe audition The entire show must be scanned to get an accurate reading. If a show or movie’s Loudness levels are too high or low, they must be adjusted to the correct specification. Loudness and audio peaks work in tandem with each other: 1LKFS = 1LUFS = 1dbfs. Fixing the loudness issue involves raising or lowering the overall audio levels to within the audio specs, while still keeping the audio peaks in spec.
Q: My movie was rejected in QC for mono audio, even though I know the movie is in stereo. What do I do?
A: This is a common problem often found in quality control processes. Incorrectly outputting to a final self-contained Quicktime file will cause stereo audio to output as mono. During Davinci Resolve, or Adobe Premiere file export, the audio being exported must be panned. These programs have audio mixers that contain sliders / knobs that have to be set for stereo audio, They must be panned left for left channels & vice-versa for right channels. Additionally files containing more than 2 channels must have audio tracks output to the correct corresponding channels for export. Editing programs default all outputs to Channels 1 & 2. Additional tracks on exported files will not recorded to the correct tracks if the file is not exported correctly. We offer audio & video fixing, conforming, and outputting, as part of our Finishing Services, and can help with any issues such as these that need to be corrected in order to pass QC
Q: What are the different sets of audio tracks that make up the audio configuration?
A: A project being submitted for Quality Control could have many different combinations of audio tracks. For Movies there are usually up to 4 different sets of audio tracks. They are:
1. 2.0 Stereo Mix (2 channels)
2. 2.0 M&E Mix (2 channels)
3. 5.1 Full Mix (6 channels)
4. 5.1 M&E Mix (6 channels)
So there may be up to 16 audio channels on a movie file. Which you use will depend on what the distributor or network is asking for. For each set of audio tracks listed above, a separate QC “Pass” will be performed. Each pass consists of watching the movie all the way through and noting any issues found.
Q: What is an “M&E” track and what can cause it to be rejected?
A. M&E refers to “Music & Effects.” In an M&E track all audio that is on the 2.0 stereo mix track (or 5.1 Full mix) is present except dialogue. The reason for this is for dubbing the movie or show into other languages. All other audio is present, the audio dubbing facility just has to add dialogue.
An M&E track can be rejected for “Missing effects in M&E” which means any sound effect that is present in the full mix track that is not also present in the M&E track. Examples of missing effects in M&E could include footsteps, doors opening and closing, tapping on a desk, hand clapping or any type of sound effect. All effects must be present in M&E tracks. We specialize in fixing missing effects in M&E, even without source files if necessary. You can learn more about our Audio fixing at our Audio QC & Post page.
Q: What are the correct “specs” for a 5.1 mix?
A: Officially there are no written specifications for a 5.1 mix per se; which is unlike other video and audio specs that SMPTE (The Society of Motion Picture and Television Engineers) has defined over the years. However, all the large studios produce 5.1 mixes in the same way.
The first two tracks of the mix are called The Left (Ch. 1) & The Right (Ch. 2) Tracks. These will contain various music and effects but no dialogue. Ch. 3 is the Center track which is usually dialogue only, and often, the only track with dialogue. Ch. 4 is called LFE or “Low Frequency Effects” track. This should be only deep bass sounds, which would normally come from a subwoofer. Both the Center and LFE tracks must be mono as they are one track each. Chs. 5 & amp; 6 are the “Left Surround / Right Surround” tracks. These go to the speakers in the back of the room in a “Surround” mix. They will also contain various music and effects but no dialogue. In a simple 5.1 mix, the stereo pairs Chs. 1 & 2, and 5.& 6) will have the full M&E on both pairs but at different levels (front speakers higher) but some movies will pan the effects around so some of the effects may be coming from the speaker behind you.
Mistakes on a 5.1 track that we often find (Which the distributor or network may approve) include.
1. Dialogue on any track other then “Center” which is the only place it should be
2. Music and / or effects in “Center” track which should be dialogue only
3. LFE track not containing Low Frequency effects only, or LFE missing completely.
4. Left / Right and or Left Surround / Right Surround tracks not being in stereo.
We can work with you to get your 5.1 mix correct.
Q: Our Deliverables lists includes Audio Stems. Is this part of The QC?
A: Audio Stems are separate “D,M,E” (Dialogue Music & Effects) files which are individual audio tracks (.Aiff, or .wav) These files can be used to re-mix the audio of the movie. These are delivered separately from the final Quicktime file that is the movie, and are not a part of the QC Report.
Q: We got a rejection for “Missing Effects in M&E.” How did this happen & how do we fix?
A: The M&E track is “Music & Effects” only. As stated above, it is used for the purpose of dubbing a film into another language. The M&E track should contain all the audio that is in the full mix track, except English (or whatever language the movie is in) dialogue. M&E tracks need to be “fully filled” in order to be approved. Often, the M&E track will not contain effects that are in the full mix tracks; these all need to be present.
Big-budget films re-create all the dialogue and effects in a movie in post-production. Low-budget filmmakers cannot afford that and use the dialogue directly from the shoot. In this instance, the sound effects that came through the microphones while shooting were used in the final mix. If a character is talking during an effect, it cannot be used in M&E. An editor would not be able to “cut around” the dialogue during the effect. That effect would have to be recreated. This is one of the Finishing services that we provide.
Q: What are the specific things that should be in an M&E mix and what should be left out?
A: We have compiled a page that gives you the exact specifications for an M&E mix as part of the industry standard. Some distributors will have different requirements and you should check with them. Here is a standard list of specific M&E requirements.
Audio Specifications for an M&E (Music & Effects) Track for Film & TV
Q: Our Audio mix has ADR issues, specifically loose ADR, what does this mean?
A: ADR stands for Audio Dialogue Replacement. Often when movies are made, the dialogue that is recorded through the boom mics is less than ideal for the final mix. The film’s producers will use ADR or “looping” to improve the sound of the dialogue in post. The actors go to a studio, watch scenes and say the lines into a microphone, repeating what they said in the original daily shoot footage. Once all the dialogue has been rerecorded, it is “replaced” back into the sound mix of the movie. Problems can arise when the sound sync between the original dialogue and the ADR dialogue doesn’t match. On some occasions, the dialogue can go in and out of sync during a single sentence. This may occur when transferring original footage to a different timecode. Loose ADR can be fixed either by adjusting the sync for full scenes or the entire mix, or by painstakingly editing every line of dialogue where the sync issues occur.
Q: Why should I hire your company instead of one of the other (bigger) companies out there?
Most Experience, Fastest Turnaround, and Best Prices. What more do you need? I started this company back in 2007 because I knew I could deliver exactly that. In that time, we have worked with a large majority of the companies in Hollywood and worldwide that provide Video content. We have a very long list of past Clients & Projects. When you hire QC Central, you are hiring an owner with over 33 years of experience in Broadcasting, Post Production & Quality Control.
You have direct access to the owner of the company virtually 24/7. You can call anytime with any questions you may have before, during, or after the job. Our QC standards are also the highest in the industry.
Q: OK we are ready to send your are project for QC, What exactly do we need to send?
A: Glad you asked. We have a page that answers that very question in fine detail it’s called What You Need To Send Us For Film QC. Please refer to this sheet for how to proceed. Of course we are also available to answer any additional questions. Email text or call anytime.
Thanks for reading this FAQ for Audio Post Production QC. Please contact any time if you have other questions.