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Craig Alan
levels
on Sep 5, 2016 at 3:19:14 am

From the SD 302 manual:

"The 302’s scale is designed for digital recording devices, providing maximum information between -30 dBu to 0 dBu which is where typical peaks occur (-50 to -20 dBFS). This allows the user to record with a full 12 to 20 dB of headroom while in the ne-resolution green-colored part of the meter. Additionally, the meter color changes to orange at 0 dBu and red at +8 dBu. These color changes correspond to -20 dBFS and -12 dBFS respectively, which are commonly used recording levels for today’s digital recording devices."

I have often heard it recommended on the forum to record at the maximum level possible, without clipping of course. I know in NLEs it is recommended to aim for -6 which is the same type of meter used on the camcorders. Obviously you need to allow for the proper headroom if you are not in close collaboration with the source. But why aim for a peak of 0 on the mixer if you can record at say +4 +8 or +12? If it's not clipping and not distorted sounding through headphones what would be the concern?

Mac Pro, macbook pro, Imacs (i7); Canon 5D Mark III/70D, Panasonic AG-HPX170/AG-HPX250P, Canon HV40, Sony Z7U/VX2000/PD170; FCP 6 certified; FCP X write professionally for a variety of media; teach video production in L.A.


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Richard Crowley
Re: levels
on Sep 5, 2016 at 2:04:47 pm

But why aim for a peak of 0 on the mixer if you can record at say +4 +8 or +12? If it's not clipping and not distorted sounding through headphones what would be the concern?

Because we operate in the "Real World"(TM) where unexpected things happen. If you are sitting at your NLE and mixing down your tracks in the comfort of Hindsight, you can target for 0dB FS if you like. In fact, most popular "music" that is produced in recent decades, and most radio stations are eager participants in the "Loudness Wars" where they squezee every last bit (in all senses) out of the audio level. If you look at the waveform of most any popular music from the last 30 years, it looks practically solid with peaks within a few tenths of a dB away from Full Scale.

But when you are out on location recording something, you never know when something will happen that will produce an unexpected peak. Back in the bad old analog days, magnetic tape was pretty forgiving of unexpected peaks. Some people even LIKEd the sound of magnetic tape driven into saturation and they still make analog mag tape and keep those old monstrosities running just for that "tape sound".

But here in the Digital Age, 0dB FS is FULL SCALE. And that is a HARD limit. When your'e out of bits, you're dead in the water. There is ZERO HEADROOM. So the only way to keep your track from hitting that 0dB FS ceiling is to record with peaks down at some safe level. Now, certainly WHERE your safe recording level target is depends on what you are recording.

If you are recording excitable play-by-play announcers at a sporting event, you must remember that they are quite likely to yell into the microphone at any moment. OTOH, if you are recording the oral history of a frail 103 year old grandmother, you probably need some extra gain to overcome the low sound levels, and you are pretty safe that she won't suddenly jump out of her chair and start yelling.

The SD 302 is labeled in the "old style" familiar to generations of sound recording professionals who grew up using analog recorders. Traditional VU meters had the reference of "0dB" up around 75 or 80% of full-scale. That means that if your target level is -20dB FS, then that is labeled "0 dB" on the SD302. Which is handy as -20 dBFS remains the preferred target when you have good, quiet gear like Sound Devices.

People who are stuck with using lesser ("pro-sumer" or consumer) gear have taken to using -12dB FS as a standard target because they just don't have the kind of working dynamic range of the top of the line gear like Sound Devices, et.al. And the higher noise floor goes along with the limited "metering" available, perhaps just a few( 4~10) LEDs which just adds insult to injury by making the job of monitoring levels even more difficult.

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.


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Craig Alan
Re: levels
on Sep 5, 2016 at 5:13:36 pm

Thanks Richard for this comprehensive response. It's also my actual practice in that I aim for higher levels only in a controlled environment and in short form films where we can reshoot if something, including audio clipping, takes place. In live events and on location, I aim for 0 on the mixer. I also only aim for -6 on the camera as a peak not as an average. In most cases, this provides enough headroom. And when I think about it, the SD302 is called a "field mixer" not a studio mixer. I also find that monitoring with headphones is of equal importance since even without hitting the limiter, audio can sound sweet or muddy or even distorted.

Mac Pro, macbook pro, Imacs (i7); Canon 5D Mark III/70D, Panasonic AG-HPX170/AG-HPX250P, Canon HV40, Sony Z7U/VX2000/PD170; FCP 6 certified; FCP X write professionally for a variety of media; teach video production in L.A.


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Richard Crowley
Re: levels
on Sep 5, 2016 at 2:16:33 pm

Just coincidentally, these were referenced in a similar thread over on the dvxuser forum:

Lineup basics for dB:





Lineup basics for PPM:





And coincidentally, I just get one of those Behringer CT100 cable testers which include a test tone oscillator. It is quite a solid little piece of test gear and quite cleverly designed. I really like it. Recommended,

---------------------------------------------------------------------------------
Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.


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Ty Ford
Re: levels
on Sep 6, 2016 at 5:18:27 pm

Hello Craig and welcome back to the Cow Audio Forum.

Yes, Richard's response is right on. (Thanks Richard)

Some of the older digital cameras like the PD150, had XLR connectors, but had semi-pro fron't ends operating at -10 consumer level rrather than at 0, +4 or +8. Once I figured that out, trying to feed clients' camcorders got a lot easier.

The Sound Devices 442 has mic, -10 and 0 (or +4)line level switches at the output XLRs. You have to recalibrate if you switch, but doing so gets rid of the "soft front end" problems referred to by people running into distortion problems.

FWIW, I usually set my Sound Devices limiter for -10 and regularly hit peaks at -12. Occasionally, a peak will pop up to -10 or higher and "tickle" the limiter light.

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Craig Alan
Re: levels
on Sep 8, 2016 at 8:42:24 pm

So you never aim for positive +4 +6 +8 (as peaks) even in controlled conditions?

Mac Pro, macbook pro, Imacs (i7); Canon 5D Mark III/70D, Panasonic AG-HPX170/AG-HPX250P, Canon HV40, Sony Z7U/VX2000/PD170; FCP 6 certified; FCP X write professionally for a variety of media; teach video production in L.A.


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Richard Crowley
Re: levels
on Sep 15, 2016 at 11:56:21 am

There is no hard and fast rule. You must use your own judgement to decide the risk vs. benefit of recording at higher average levels. Here is one of my favorite parables which just happens to apply here...

There was once a magical land where the king resided in fabulous castle with his family and royal courtesans. The castle had an amazing view of the kingdom from the top of a craggy mountain. You could see for miles in every direction. The downside was that the only way up to the castle was a narrow road which in places was hewn into the side of the rocky cliff. The roadway was barely wide enough for the king's carriage and team of horses.

At the retirement of his most trusted driver, it came time to interview candidates for the job. The king asked each candidate: "How close to the edge of the road can you safely drive my carriage with my family in it?" Candidate A said: "I can drive within 1 foot of the edge safely." Candidate B said: "I am so good, I can drive within 6 inches of the edge safely!" But then candidate C said: "Honorable King, with such a precious cargo as your wife and children, I would stay as far away from the edge as possible." Guess who got the job.


---------------------------------------------------------------------------------
Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.


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Bruce Watson
Re: levels
on Sep 9, 2016 at 4:46:33 pm
Last Edited By Bruce Watson on Sep 9, 2016 at 5:34:31 pm

[Craig Alan] "This allows the user to record with a full 12 to 20 dB of headroom while in the ne-resolution green-colored part of the meter. Additionally, the meter color changes to orange at 0 dBu and red at +8 dBu. These color changes correspond to -20 dBFS and -12 dBFS respectively, which are commonly used recording levels for today’s digital recording devices."

Not a very elegant description. What they are saying, more or less, is that the 302's meter is a Vu meter (so called dBVu units). A completely different thing, and a different scale, than digital dBFS.

What I do is use the calibration tone on the mixer (mine is a MixPre-D which is one step down from the 302). Use that calibration tone to set the recorder (camera, dedicated recorder, or whatever is recording) to -12 dBFS. Then completely ignore the recorder and do all adjustments from the mixer. I typically aim for a dialog peak of +8 dBVu on the mixer, which gives a corresponding -12 dBFS on the recorder. This gives me 10 dB of headroom before the mixer's limiters kick in at +18 dBVu (which is 2 dB before the recorder's 0 dBFS).

Done this way I've found my recording chain to be more or less "clip proof". IOW, I've never had it clip, and seldom seen the limiters actuate. It takes something like a cooking instructor setting down a glass mixing bowl on a granite countertop considerably too hard to kick the limiters in; I've never had a voice do it.


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Ty Ford
Re: levels
on Sep 9, 2016 at 10:55:17 pm

Bruce,

Interesting. I use the tone from any of my Sound Devices 442 and MixPre-D mixers or 664 recorder to -20 on cameras or external recorders.

I normally run peak levels to -10 to -12 on the mixers and output of the 664.

I set the limiter threshold on the Sound Devices devices to -12. This gives me bump and shriek room which will also be caught by the Sound Devices limiters. I've found this works very well.

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Bruce Watson
Re: levels
on Sep 10, 2016 at 1:47:01 pm

[Ty Ford] "I set the limiter threshold on the Sound Devices devices to -12. This gives me bump and shriek room..."

My understanding (that is, my interpretation of what SD tech. support told me years ago) is that the MixPre-D doesn't clip until +20 dBu on the MixPre-D meter (second to the last LED). And the lowest you can set the limiter is +8 dBu. So maybe you mean +12 instead of -12? Or maybe I'm just misunderstanding what you're saying.


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Ty Ford
Re: levels
on Sep 10, 2016 at 2:08:25 pm

yeah, +12, below +20.

Thanks,

Ty

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Craig Alan
Re: levels
on Sep 10, 2016 at 4:08:44 pm

Thanks Ty,
setting the limiter below+20 to +12 makes sense to me. So getting back to my original question:

"I normally run peak levels to -10 to -12 on the mixers and output of the 664."

are these your peak levels or did you mean +10. If 0 on the mixer is calibrated to -20 on the camera then -12 on the mixer is going to be really low on the camera's meters.

I set the calibration to 0mixer=-20camera and then aim for 0 +4 +8 on the 302 for peaks depending on how controlled the audio source. On less controlled shoots I aim for 0 peaks on mixer which has a lot of head room on camera if calibrated to -20.

And yes I was one of those Sony PD owners a while back who noticed that before hitting 0 on the camera's meters it was already distorted. So I aimed for lower levels.



Mac Pro, macbook pro, Imacs (i7); Canon 5D Mark III/70D, Panasonic AG-HPX170/AG-HPX250P, Canon HV40, Sony Z7U/VX2000/PD170; FCP 6 certified; FCP X write professionally for a variety of media; teach video production in L.A.


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Bruce Watson
Re: levels
on Sep 10, 2016 at 6:32:05 pm

[Craig Alan] "setting the limiter below+20 to +12 makes sense to me."

Notice from the SD docs on the 302's input limiters: "+18 dBu threshold, 20:1 limiting ratio..." So SD ships them with the default limiter threshold at +18 dBu. That's because of the massive 20:1 ratio. The 2 dB between activation of the limiter and the 302 actually clipping is huge. Not a brick wall, but you can see it from here. It's highly unlikely you'll encounter anything that will go through the limiting process and still make it to clipping. So setting the limiter threshold to +12 dBu, which is 6 dB lower, is effectively tossing out that 6 dB of gain. Yes, it's technically headroom, but practically nothing short of an explosion will be able to make use of the upper range of that headroom. And if you're recording explosions, please be careful!

That said, just because SD expects people to use the mixer this way doesn't mean anyone has to. That's why SD makes the limiter threshold adjustable. I'm just sayin' that setting the limiters to +12, and making your average dialog peaks 0, that'll work too. You're not doing anything that's wrong.

I only answered that I typically set my average dialog peaks at +8 because you asked the question in your original post:

[Craig Alan] "But why aim for a peak of 0 on the mixer if you can record at say +4 +8 or +12?

My answer is that I personally aim for a peak of +8 on the mixer. Because I can't think of any reason not to, and SD couldn't either when I asked them. Limiters at +18 dBu, calibration tone on the recorder at -20 dBFS, and average dialog peaks around +8 dBu on the mixer (which translates to -12 dBFS on the recorder) seem to be the way SD expects the mixer to be used in my understanding.


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