Audio Level for Recording on Zoom H6 or equivalent
I'm relatively new to Creative Cow, but have spent several hours on internet searches and don't have a satisfactory (or direct) answer to a simple question I have. Perhaps I simply don't understand the available explanations and so I would appreciate someone with the patience to explain this to me.
I've read that there are general guidelines for the dB levels when recording audio. These rules of thumb differ for different recording settings (film, broadcast, dialogue etc) but generally fall somewhere in the -20 to -6 dB range. The main reason for this is to avoid clipping (which is when audio goes above 0 dB and gets distorted).
I am struggling to understand the rationale for a lower bound for the audio. Intuitively to me, the ideal would be to record at as soft a level as possible to eliminate background noise maximally, and then adjust the audio to a pleasantly audible level in post. Why then should we be aiming for something in the ball park of -20 dB? Is it because volumes below that are not audible?
I've just come off a shoot today and tried recording at -40 dB and -10 dB respectively on a Zoom H6 (different scenes, to be fair), and found that comparing the two in post, once they'd been adjusted to sound the same in terms of volume, that the recording at -40 dB was clearer (less noise). Even if it took more adjustment to arrive at a suitable audible level (it was soft when first imported).
I should mention that at the -40 dB recording, it is still possible to hear the playback reasonably clearly when the recorder's playback volume is at 100.
I'm struggling to make sense of this. Is it that:
1. Not all meters on all recorders are calibrated the same, and so -40 dB for me may be -8 dB for another recorder?
2. The logic behind 'record as soft as possible to minimise noise' is mistaken?
3. Should you be basing your judgement of a good take (volume wise) on whether it sounds right through the headphones, or a mixture of headphones and meter, or purely meter?
Thank you for your help.
Note first that there is a big difference between where we RECORD things vs. where we end up MIXING them.
Boiled down to its essence:
Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.
afaik, the recording level is usually bounded by two things, noise floor and dynamic range.
Noise floor is always there, its just at a lower volume so you don't normally hear it.
If the native noise floor of a recorder is -80db and the mic noise floor is -60, then your final noise floor is actually the poorest thing in the audio chain; in this case, the mic at -60db.
When do you start hearing hiss then? Some mics need phantom power and a lot of it to get above the noise floor. Other plugin
power mics need a strong signal to get above the noise floor. All of this is very relative. That is why you can't record something far away and simply turn up the gain.
The other extreme is distortion or voltage levels outside the parameters of either the mic or the recorder. In the digital
world, its a hard limit. analog can push a little past 0db.
So, the best way to answer your other question is that 'normally' the human voice has a certain dynamic range when it whispers, talk normally, and yells. -23db RMS is a good place to start because it lets a person talk both softly and loud without having to compress/limit or clip the audio which is probably what happened to your -10 recording). An added bonus is that the normal talking will usually automatically top out around -12/-10db making post a cince as youtube is -16LUFS and theatres are -23LUFS, all your audio will already be close to the target and be the right volume when you sit in the chair.
There's some sound devices that can analog limit though. So, you may be wondering, "why don't I just record everything at -1db and let my sound devices soft limit for me?" The answer is, beyond a certain ratio like 4:1, voices will sound unnatural. I don't go beyond 4:1 sfx and 2:1 dialogue personally but your mileage may vary. People's ears get tired when dynamic range is too large in a 2 hour movie. Perhaps you've noticed this in some independant films.
A good reason why someone would want to record at higher levels while leaving headroom for sudden spikes (eg. -20dB to -12dB) is when using cheaper mic cables or preamps that introduce noise. An example I’ve personally dealt with is plugging directly into a “prosumer” camera’s XLR ports, which has circuitry that isn’t designed for recording audio like a dedicated digital audio recorder. There usually will be a hiss that is present at (and I’m picking a random number) -50dB with the on camera’s audio gain controls at the halfway point. Not to mention any other noise from an air conditioner or computer fan or whatever else was in the room on location that will be picked up as well.
If I were to record an interview with this configuration and the interviewee being recorded was between -40dB to -30dB, and I go to compress and normalize in post to something more standard like -9dB to -6dB, then that -50dB hiss will be brought up to -20dB or so. Even with a good noise reduction plug-in, that is less than ideal to have to “fix in post” and should be avoided from the initial recording process.
But sure, using a high quality microphone, with a nice cable, with nearly perfect mic placement to the audio source, on a professional sound stage or recording studio, and recording to a nice dedicated audio recorder with great preamps...then you absolutely could record at average peaks of -40dB and normalize it to whatever standard you need and have it sound fantastic.
I use a H4n Pro myself on anything I personally have a hand in recording (location interviews) and I still strive for a -12dB average, and settle for -20dB at the worst. And I almost always use iZotope dialogue de-noise anyway...but the cleaner the initial recording is with a high signal strength the better the plug-in works.
But I have received videos where someone recorded voice-over using a headset mic near their computer fan that was around -40dB for the peaks...by the time I normalized the audio the computer fan noise was unbareable. In the end using iZotope salvaged it “good enough” but still...ugh.