AF/AP vs ALC

[Chamber005]

So I'm wondering if using ALC on a recorder is akin to a cinematographer using AF or AP.

Personally I think there are sometimes uses for auto-focus, whereas auto aperture is a crime against nature.

Since my sound person is a novice and I usually have to just set the audio levels at one spot and then another spot and then another spot, shooting different parts of different scenes depending on the actors' actual volume or timber in a given moment, I'm wondering if auto levelling might be something worth trying.

Have any of you ever tried auto levelling? Are there any major draw backs?

Additionally, I was wondering if bigger is always better.

I can record at 16 bit 48khz or 24bit up to 96khz. I'm not too concerned with file size. Is 24/96 the better choice across the board?

 

[Richard Crowley]

Putting a boom mic on a fixed stand and expecting it to work while actors move around is equivalent to "Auto Focus". Using Auto Level-Control is almost identical to Auto Aperture. And many (most?) audio people think it is very much "a crime against nature".

OTOH, I have been known to use ALC myself for talking-head speech recording for documentary (or transcription-) grade production. ALC is NEVER a useful thing for serious music recording.

IMHO, ALC is NOT acceptable for serious production, even for speech recording. You should be rehearsing each shot anyway (for blocking, camera, lighting) and also for sound. The actors should speak (or shout or whisper, as the script dictates) and the choice and location of microphone(s) and recording levels should be adjusted accordingly.

The primary problem with ALC for speech recording is "pumping" where the ambient noise level is brought up in-between words, phrases, sentences, etc.

Of course, the primary problem with ALC for music recording is the mutilation of the dynamic range of the music.

IMHO, unless you are doing very high-end production of music programs for PBS or something, 96K recording is overkill. 48K is the standard for video and there is no compelling reason to record at a higher rate. It will just require knocking back down to 48K for editing, and it will take twice as much recording media space for no good reason.

OTOH, 24-bit recording (IF the equipment is really up to it) IS desirable because it allows a wider dynamic range to give you more "breathing room" between the "mud" (noise) at the bottom end and full-scale clipping at the top end. Especially for live concerts, I always record 24 bit because it is practically impossible to predict where the peak sound level will be. Even if you have a chance to record rehearsals, etc. live performances have a common habit of ending up with higher peaks.

 

[Chamber005]

Putting a boom mic on a fixed stand and expecting it to work while actors move around is equivalent to "Auto Focus". Using Auto Level-Control is almost identical to Auto Aperture. And many (most?) audio people think it is very much "a crime against nature".

OTOH, I have been known to use ALC myself for talking-head speech recording for documentary (or transcription-) grade production. ALC is NEVER a useful thing for serious music recording.

IMHO, ALC is NOT acceptable for serious production, even for speech recording. You should be rehearsing each shot anyway (for blocking, camera, lighting) and also for sound. The actors should speak (or shout or whisper, as the script dictates) and the choice and location of microphone(s) and recording levels should be adjusted accordingly.

The primary problem with ALC for speech recording is "pumping" where the ambient noise level is brought up in-between words, phrases, sentences, etc.

Of course, the primary problem with ALC for music recording is the mutilation of the dynamic range of the music.

IMHO, unless you are doing very high-end production of music programs for PBS or something, 96K recording is overkill. 48K is the standard for video and there is no compelling reason to record at a higher rate. It will just require knocking back down to 48K for editing, and it will take twice as much recording media space for no good reason.

OTOH, 24-bit recording (IF the equipment is really up to it) IS desirable because it allows a wider dynamic range to give you more "breathing room" between the "mud" (noise) at the bottom end and full-scale clipping at the top end. Especially for live concerts, I always record 24 bit because it is practically impossible to predict where the peak sound level will be. Even if you have a chance to record rehearsals, etc. live performances have a common habit of ending up with higher peaks.

Hmm. So even though I'm printing to DVD (16bit/48khz), do you think it's a good idea to record at 24bit/48khz as that will leave me more room in post to toy with the audio?

Also thanks for the tip on ALC, with the advent of instant auto focus and face detection tech, auto foucsing with a camera isn't so much a horrendous act -- but it sounds like ALC is much more akin to auto aperture (with the "pumping" action). I'll just continue to do things the way I've been doing them (like you said, shooting for certain levels in addition to having a couple of wild tracks specifically designated for potentially distorted or muted line readings).

 

[Richard Crowley]

Hmm. So even though I'm printing to DVD (16bit/48khz), do you think it's a good idea to record at 24bit/48khz as that will leave me more room in post to toy with the audio?

Yes, absolutely. Recording in 24-bit gives you the latitude to record even unpredictable levels and stay in the "Goldilocks zone", yet still adjust the mix for exactly what you want. This assumes that your NLE software will accommodate 24-bit audio tracks.

 

[Noiz2]

Hmm. So even though I'm printing to DVD (16bit/48khz), do you think it's a good idea to record at 24bit/48khz as that will leave me more room in post to toy with the audio?

Absolutely. It gives post more to work with and it does sound better.

Also thanks for the tip on ALC, with the advent of instant auto focus and face detection tech, auto foucsing with a camera isn't so much a horrendous act -- but it sounds like ALC is much more akin to auto aperture (with the "pumping" action). I'll just continue to do things the way I've been doing them (like you said, shooting for certain levels in addition to having a couple of wild tracks specifically designated for potentially distorted or muted line readings).

The problem with both (among others) is that it's a lazy unprofessional way to work. Auto focus isn't as awful as it used to be but if I'm hiring a DP it's not as a button pusher, I want them to frame and focus the shot. If I wanted the cameras computer to decide how I wanted my film to look I could use a trained monkey to push the button. Still's and doc's are a slightly different story but still I want the DP/ cameraperson to pick the focus. AGC is rarely useful for something you want people to hear. It's good for sync tracks when your using the on camera mic to generate a track that your going to replace. But every time it gets quiet it's going to pump up the noise to ugly levels. The other problem with every AGC I have seen and many consumer/ prosumer "limiters" is that the are SLOW. They miss the peak you wanted them to catch and then over correct after the fact. So instead of having a short bit of distortion you end up with the same distortion and then a drop out and recover as the AGC reacts late to the level. If they actually looked ahead and acted smoothly I could see them being much more useful in doc situations. The pricey "auto mixers" may work better but I have never used one and I don't think they would have much use in production. Maybe if you were doing one of those 15 wireless lav party scenes to mix a quick and dirty dailies mix????