Audio and the AF100

[TheDingo]

This strikes me as similar to saying the WFM should never go above 75% for fear of a bright light suddenly appearing.

The scenarios are not the same. With audio, if somebody gets a little to close to a mic, or is a little too enthusiastic with their performance, you run the risk of clipping the audio and having to start over again. By ensuring sufficient "headroom" there is no risk of ever clipping at the recorder stage.

You're recording 16/48. If you're setting your maximum dB at -12, then when you bring the volume up 10 or 12 dB while finishing it you're guaranteed to end up with noise.

Not true at all. Remember that by setting your recording level at -12 dB, you are recording EVERYTHING 12 dB lower than if you were to record at 0 dB.

So normal conversation gets recorded at -12 to -24 dB, a person whispering might be recorded at -36 dB, and room ambient is recorded at -60 dB.

When you boost everything by 12 dB in post, the normal conversation is now 0 to -12 dB, the person whispering is at -24 dB, and room ambient is now -48 dB. It all sounds perfect with no distortion, and no noise at all other than room ambient, which would always be -48 dB if that is what the actual room ambient is.

If it was a super quiet environment, where the room ambient is -64 dB, then you would need a mixer/recorder ( or camera ) with at least 76 dB of dynamic range to be able to reproduce everything accurately, including the super quiet room ambient of -64 dB.

My Panasonic HS-700 has a noise floor of -82 dB, so it would actually be up to the task of faithfully recording this super quiet room, but my HMC-150 with a noise floor of -63 dB would fail when it comes to reproducing the super quiet ambient room sound.

Professional recorders like the Sound Devices recorders have noise floors of -100 dB or more, so you could record at -20 dB and still have another 80+ dB of audio range to reproduce whatever you are recording.

Where you can run into trouble is when the mixer / recorder / camera has poor audio circuitry and a high noise floor. My Canon 60D camera ( which I owned for 3 months ) had a noise floor of only -53 dB, which bugged the crap out of me, because it meant that I could not make any mistakes when recording, or I had to sacrifice some of the "headroom" to gain back some usable dynamic range. My GH-2 camera has the same noise floor as my HMC-150, which is around -63 dB, which is 10 dB better.

Currently I haven't had the budget for a Sound Devices recorder, and I think it will be a couple of years before I do, so I get by with the 60+ dB of range my current portable recorders / cameras provide.

I do plan on buying a Sony M10 portable recorder at some point later this year, because it is supposed to have a noise floor around -85 dB, and costs about $230 at B&H Photo in New York. This is 20 dB more dynamic range than my GH-2 or HMC-150 cameras, and would be great to have when shooting Indy films.

 

[TheDingo]

Wow she looks young, and probably talented as all get out...

Nice job Shooter. What are the mics you used to record the piano ?

( I will check your audio files some time tomorrow )

 

[Doc Bernard]

The Dingo and Jeff

Sent a link to the files in a PM

Here are pix of the set up. Forgot to get a picture of the AF102 because I was so focussed ( freaked out) on the audio set up and also...I was setting up lights, camera and the mics by myself! All had to be set up in 2 hours before the shoot.

Shot 720p PAL. ( pixel peepers note ..lack of banding in the ungraded frame grab) I have never yet seen any banding on anything I have shot BTW.

Nice!!!!!!!! CK-7 mics!!!!!!!!! I QC'd those (in other words, those mics were in my hands before!)

 

[Shooter]

Wow she looks young, and probably talented as all get out...

Nice job Shooter. What are the mics you used to record the piano ?

( I will check your audio files some time tomorrow )

I used 1 x Avantone CK-6 and 1x Avantone CK-7 . Essentially identical .

Pianist is 16 y.o and you judge if she has talent.

 

[Doc Bernard]

Okay, angles were off. They both look like our 7's

 

[Shooter]

Okay, angles were off. They both look like our 7's

Trick photography!

I was rapt with these mics....

I thought they had a lovely warm sound and they certainly handled the massive dynamics of the Steinway.

As promised by the vendor...they really "punch above their weight."

(wot do I know?. Iam an audio amateur ....but I know what I like.)

BTW: Doc Bernard did QC my mics. I have his siganature on the test page of my owners manuals. ( Cool)

 

[Doc Bernard]

(....but I know what I like.)

And that's all that matters. It's your ears that you can only really judge by.

 

[nadir3000]

The scenarios are not the same. With audio, if somebody gets a little to close to a mic, or is a little too enthusiastic with their performance, you run the risk of clipping the audio and having to start over again. By ensuring sufficient "headroom" there is no risk of ever clipping at the recorder stage.

Right. And by shooting significantly underexposed, you never run the risk of overexposure. Same issue.

When you boost everything by 12 dB in post, the normal conversation is now 0 to -12 dB, the person whispering is at -24 dB, and room ambient is now -48 dB. It all sounds perfect with no distortion, and no noise at all other than room ambient, which would always be -48 dB if that is what the actual room ambient is.

No noise? Experience tells me otherwise.

The issue isn't the dynamic range of the available sounds, or even the dynamic range of the mixer, it's the sample depth - 16 bits. I'm not sure what the noise floor is for the AF100, but let's say it's -60 dB. That dynamic range is sampled at a depth of 16 bits, and if you stretch those bits the quality diminishes.

Think of it as a gradient from black to white. If that gradient takes 100px to get from black to white it will look smooth when scaled at 100px or less. If you stretch that gradient out to 300px, you see the steps between shades. If you turn the gain down on a recording, it won't lose detail or resolution. If you turn it up, you get noise.

Doing any editing on 16/48 is risky. Often it's not a huge deal, certainly if it's subtractive and not additive, but 6dB of gain starts to push the resolution of the audio. Since we're talking about recording music, where the quality of the sound is significant, I would advise using audio sampled at greater depth. Barring that, I would make sure to use as much of those 16 bits as you can.

Have the musician play the loudest passage, particularly with the lowest notes as they'll have the biggest transients. Give yourself 3 or 4 dB over that (6 if you're dealing with a seriously dynamic sound source, such as the human voice, or just nervous about it), and try to avoid adding gain or EQ.

 

[Shooter]

Right. And by shooting significantly underexposed, you never run the risk of overexposure. Same issue.

Ah ha! Now you are in my territory!
If you shoot seriously under exposed ...you are correct ( you wont risk over exposure) but you do lose the detail in the shadows. The detail will become unrecoverable and you can only add visual noise. Protect the blacks (shadows) and protect the whites ( highlites)

 

[TheDingo]

Right. And by shooting significantly underexposed, you never run the risk of overexposure. Same issue.

Your exposure analogy is more appropriate. If you under-expose by 2 F-stops using a camera that theoretically has a huge dynamic range ( lets say 18 stops ), you are sacrificing 2 F-Stops to capture a 12 F-Stop image, and still have 4 F-Stops of exposure range to spare.

Yes, I know that no such camera exists right now ( except for maybe the new RED Epic in HDRX mode ), but there are recorders in the audio world that have this huge dynamic range that far surpass the audio requirements we need for film-making.

No noise? Experience tells me otherwise.

And my experience ( and reading posts from the fanatical audio enthusiasts on the Tapers Section forum: The Tapers Section Website ) tells me the exact opposite. It does not matter how low you set your recording level in the digital world, provided your equipment has the dynamic audio range to properly capture what you want to record and that you choose an appropriate sampling rate.

 

[jmarkham]

Ah ha! Now you are in my territory!
If you shoot seriously under exposed ...you are correct ( you wont risk over exposure) but you do lose the detail in the shadows. The detail will become unrecoverable and you can only add visual noise. Protect the blacks (shadows) and protect the whites ( highlites)

That is a perfect analogy/analysis. Depending
on the material, it may not matter. But, for piano
forte and these pieces, it most certainly does.
You want to capture all of the dynamic range
(aka latitude).

 

[nadir3000]

Your exposure analogy is more appropriate. If you under-expose by 2 F-stops using a camera that theoretically has a huge dynamic range ( lets say 18 stops ), you are sacrificing 2 F-Stops to capture a 12 F-Stop image, and still have 4 F-Stops of exposure range to spare.

Yes, I know that no such camera exists right now ( except for maybe the new RED Epic in HDRX mode ), but there are recorders in the audio world that have this huge dynamic range that far surpass the audio requirements we need for film-making.

There are certainly recorders that, used properly, will deliver more than needed sound quality. However, most of them work at 24bit, and we're talking about 16bit.

It does not matter how low you set your recording level in the digital world, provided your equipment has the dynamic audio range to properly capture what you want to record and that you choose an appropriate sampling rate.

This is easy to test. Record something such that it peaks at -60 dB into your AF100. Then add gain to the file to get the peaks up to -3dB.

Digital recording isn't infinitely flexible.

At 24bit I wouldn't worry as much about being -12dB for peaks. I tend to record a little hotter, but that's the kind of guy I am*. There's more detail, so it's more forgiving.

I think of 16bit as an output format, like h264 or mp2. If you're going to use it to record (something we all do) there is a good argument to be made for trying to use as much of that dynamic range as possible. There's also a really good argument for processing it as minimally as you can.




* the kind of guy who owns a limiter.

 

[TheDingo]

There are certainly recorders that, used properly, will deliver more than needed sound quality. However, most of them work at 24bit, and we're talking about 16bit.

16-bit audio files have a theoretical dynamic range of 96 dB, and a practical dynamic range in the mid 80's. ( dependent on the quality of the hardware ) Using a recording level of -12, with good equipment you still have a usable dynamic range of 70+ dB.

The AF-100 likely performs about the same as my HMC-150, which means that you only have about 51 dB of dynamic range to work with if you use a recording level of -12, which is kind of slim for musical performances. ( like Shooter's piano recording ) In this instance I agree that using a higher recording level ( say -6 dB ) would help to retain more of the musical performance. A separate HQ recorder would be a better solution than recording with the camera.

At 24bit I wouldn't worry as much about being -12dB for peaks. I tend to record a little hotter, but that's the kind of guy I am*. There's more detail, so it's more forgiving.

24-bit audio has a theoretical dynamic range of 144 dB, and a practical range of 124 dB.

24-bit audio will only make a difference if the hardware you are recording with has a very low noise-floor ( lower than -80 dB ), otherwise self-noise from the recording gear kills the benefits of using the 24-bit format when recording.

I would love to know what the real noise-floor is for the new Sony cameras ( F3 and FS-100 ), as I haven't been that impressed with the audio from the Panasonic gear ( with the exception of the consumer HS-700 camera ), and would like to know how Sony compares.

 

[jmarkham]

Now that I look at the picture of the mic positions ... what was the rationale for placing the left microphone over the plate?
It's recommended that you remove the lid if you do this.

jeff

 

[Shooter]

Now that I look at the picture of the mic positions ... what was the rationale for placing the left microphone over the plate?
It's recommended that you remove the lid if you do this.

jeff

That would be my gross inexperience and the short set up time mostly!

Rationale for the simple set up ( and I saw many in my research including one similar to what I used) was mainly to get sound from the bass and treble strings with mic coverage from the cardiod overlap getting everything in between.

Just about to listen to the final files you sent me. I saw what you meant in the mov you sent me.

 

[Shooter]

Note : I sent Jeff some audio files and he was kind enough to take a listen and do some audio post on them. He gave me a lot of advice (mostly about what I did wrong) but thats how you learn.

Hi Jeff

The audio post you did on my recordings sounds amazing. I have no idea what or how you did to them , but seems like you have opened the dynamic , tones and stereophony. Wish I had the time and budget to have given you the entire 30 minutes of performance but the client is over the moon anyway.

Despite my fumblings...your post work has shown me the possibilties and taught me a lot. I thank you.

That does not mean I am going out and selling myself as an audio guy BTW.
I will be sticking to my knitting as a cameraman director ...but I now have a bit of audio confidence and a bit of relatively capable low-end gear to do these little no-budget ($500) gigs and have a lot of fun doing so.

Hey Jeff. Time to admit I did a reasonable job of it huh???

 

[jmarkham]

Hey Jeff. Time to admit I did a reasonable job of it huh???

Absolutely Craig ... you went well above and beyond the call-of-duty for your client! It sounds good and
you stayed within their budget. Best of all, they're happy!

I'm impressed that you took the time to learn the world of audio .. instead of chucking off to the
"sound guy" ...

I would be more than happy to do post for you pro-bono .. i studied piano myself and have a soft-spot for
the instrument....

PM me.

jeff

 

[Shooter]

....and you stayed within their budget.

Actually not quite...I brought 2 mics, a field mixer, assorted mic cables...and..... I also ended up buying a new jazz guitar that caught my eye when I was in the piano shop doing the shoot.