Here are some fun facts about sweetening audio for HDTV.

Update: December 7th, 2009

Here are some fun facts about sweetening audio for HDTV.

By Nick Denke of American Production Services:    Send EMail

To start a sweetening session, most audio post houses will require one of 3 things:

1. An OMF file from an Avid Media Composer that got the audio from the HD field tapes.

2. An EDL of the audio cut and the HD field tapes.

3. A cut version of the audio, usually from the HD Online session. The OMF file is one of the most flexible ways to input audio for a session, but beware: OMF compatibility varies depending on versions of media composer and audio workstation software. Run tests before your show nears the deadline! Also make sure that the audio is clean when digitized into the Avid. Quality sometimes suffers when HD field tapes are dubbed to analog Betacam formats before digitizing. Be sure of a nice clean signal flow – make sure no distortion happens between field tape and Avid.

EDL’s are also flexible and more reliable than OMF, but are more time consuming, since the audio must be re-digitized.

Having a cut version of the audio from the HD Online session is the fastest way to get started, but offers less flexiblity on edits and number of tracks. What’s the best way to go? It all depends on your project. Get your offline editor and online editor to start a dialogue with your audio post engineer well before the session. They can work out the best method for your individual situation.

SURROUND MIXING:

Unlike SDTV, the audio for HDTV can be mixed in many different formats. 5.1 Surround can be broadcast from HDTV stations, and is the best way to mix. It includes 6 separate channels: Left, Center, Right, Right Surround, Left Surround, and Subwoofer. It is the highest form of audio on DVD also.

Mixing in surround takes more time than sweetening a standard stereo soundtrack, but depending on the complexity of sound effects in the show, it may not increase time significantly. The main problem with 5.1 surround is not the ability to broadcast it, but the ability of the videotape to play it back and the ability of the TV stations to all of a sudden upgrade all of their stereo routing to 5.1 surround routing. (That’s 6 channels where there used to be 2). HDCam, D5 and other HD formats have only 4 channels of audio instead of 6.

Dolby Laboratories has addressed this problem with the upcoming new format “Dolby E” Dolby E allows 5.1 surround audio to be compressed into a bit stream taking up the space of 2 channels of audio (stereo). That way, HDCam can record 6 tracks into 2 channels of Dolby E and have it decoded on the other end back into 6 tracks of audio. This format was shown at NAB’99 and will soon ship to the public. So what to do in the meantime before Dolby E is completely deployed? At APS, we’ve been doing a lot of Dolby Pro-Logic surround for HDTV. This way we get the surround effect to the audio and stay compatible with existing SDTV infrastructures. Pro-Logic is the traditional Dolby Surround that was first brought to consumers in the early ’90’s. It has 4 channels: Left, Center, Right, and Surround. It also encodes on to 2 channels of audio (stereo) and is completely compatible with SDTV, stereo and mono.The other option is to stay with a standard stereo or mono soundtrack. Not as much fun, but it will still be compatible with the new HDTV. Just watch out for the competition and their surround packed mixes.

Other than that, the same rules for audio for SDTV apply to HDTV. Hire good location audio mixers with good equipment, get a good sound design team for post, and your soundtrack should shine. Even with all the brilliance of the HDTV picture, the true emotion in any piece is driven by the audio soundtrack.

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