audio post-mortem, please?

P

powerdog

Veteran
OK, I can't figure out what happened and how I could have prevented it.

I recently completed a 1-hour video, heavy on interviews, and tried to be very careful about volume levels. I listened countless times with the monitor off and using a pair of very good headphones. Also with a pair of not-so-good self- powered speakers. Using what I heard and the level meter in FCP, I tried to set an equal volume for everything.

Now, I've watched/heard the DVD many times since I completed it, and nothing about the sound seemed particularly wrong.

So last night it had its "world premiere" at the small museum I did it for. A nice member-only event. They used cheap speakers and low-end amp and DVD player, and they'd done their own purchasing of DVD duplication. So it was their DVD, not one of mine.

What stood out for me was the huge range in volume from clip to clip. I'd say about 60% of the footage was fine, with 20% too low and 20% too high. This was the only time the differences were so striking.

I'm left wondering: WTF happened, and how do I prevent it w/o throwing a ton of $$ at the problem?
 
DVD duplication shouldn't affect playback volume. The duplication process is supposed to do a straight copy of data on the disk, so there's nothing that would get tweaked in the process without harming the actual playability.

See if the museum's system has a limiter or automatic level control that might foul up the playback level. Check for bad connections, worn cables, etc.

But before that, see if the same section of the program exhibits the same problem. Check their copy of the DVD, and then check yours to see if they function identically. If the problem is in the same place each time, then the problem is with the original material from which the DVD was authored.

It could be in the authoring process. When the audio was encoded perhaps there was a feature that might try to modify the volume? Perhaps an "equalize" feature?

It could be in the methods you use to monitor the audio.

For one thing, monitoring through headphones is not a good idea. It's ok in the field to make sure audio quality is OK but for actual mixdown and EQ it's not the way to go. I learned this from an engineer at Oceanway in Hollywood as well as from several others who have built impressive careers in the recording business.

It has to be on a pair of good speakers in a good room. Even the best headphones will give you a lot of false impressions about the mix and EQ.

Standing waves in a room with hard walls can cause "dead spots" and "hot spots" where listening volumes will vary from one point to the next. Sometimes these spots can be just several inches apart, depending on the size of the room, the placement of the speakers and the frequency of the sound. Try playing a test tone and slowly moving your head from one point to another and see if there's a significant change in volume. If there is a serious difference over a small distance, then something needs to change in the room itself.

Make sure the system you're doing your mixdown on is set for a flat response. Some people like to hype up the bass and treble on their speaker systems because it makes things sound brighter, punchier, etc. But by doing so they end up with a distorted impression of the actual mix -- which will end up duller and thinner.

Listening levels can affect your impression of the mix, too. For example, listening at high levels for extended periods of time can fatigue the ears, not to mention harm the hearing if done at really high levels for very long periods of time.

Check on your original mix and see if there are EQ issues that might affect the sound quality at the other end. If the museum's sound system is especially poor, then frequencies your system is playing might not be coming through on the museum's system and giving the impression of being louder or softer.

There's a ton of things to deal with when it comes to audio. It can be just as complex a color management in video.

Hope this helps!
 
Soundtrack Pro

Soundtrack Pro

Sorry posted on your thread by mistake. :S
 
Last edited:
Powerdog:
Might be the DVD-encoding. Try compressing your audio in FCP or soundtrackpro before you encode. That way the encoder has less decisions to make on its own...
 
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