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Friday, April 19, 2024

What Is 32-Bit Float Audio, and Should You Record In It?

Unlike video tech, which seems to change every 10 years or so, audio has stayed largely the same for decades. If you bought a decent microphone and interface a decade ago or more, there’s a good chance that, if it hasn’t broken, it’s still great today. But there’s one relatively new format that might (might) be worth upgrading your workflow if you make videos: 32-bit float audio.

The most common claim you’ll hear when it comes to 32-bit float audio is that it removes the need to ever set levels, where you make sure the audio isn't peaking and distorting. And that’s sort of true. But does that mean you need to upgrade all your gear to make sure that loud noises and quiet ones come through clear with no thought to level setting? Not necessarily.

To get a sense of how this tech works, I spoke with Korey Pereira, sound supervisor at Chez Boom Audio in Austin, Texas, and a freelance dialog editor who most recently worked on the latest season of Stranger Things.

Diving Into Bit Depth

Bit depth in audio refers to how many bits are available for each sample of an audio signal. For example, in 16-bit audio (like the stuff you've been listening to from CDs), there are 16 digital bits (naturally) that can describe 65,536 audio amplitude levels (volumes of sounds). 24-bit audio, meanwhile, can record over 16.7 million distinct levels. This isn’t to be confused with bitrate, which is essentially how many samples of an analog audio signal are taken each second. (For example, a 96-kHz audio file has 96,000 samples per second.)

32-bit float audio is similar to 16- and 24-bit standards, but it works a little differently. Rather than counting discrete amplitude levels for the audio signal, values are essentially encoded in a binary variation of scientific notation (sort of; engineers please don’t yell at me). So, rather than writing a number like 136,234,000, this number could be expressed as 1.36234 x 10^8. In 32-bit float, up to 23 places after the decimal and up to 8-digit exponents can be recorded.

That’s a lot of math. Does it matter to you? Probably not. But here’s the important takeaway: Under 32-bit float, a much wider range of audio values can be recorded. Vastly more than if there were simply eight new bits to play with.

To put it in perspective, 16-bit audio is capable of recording sound with a dynamic range of up to 96.3 decibels. 24-bit audio recordings can capture a dynamic range of up to 144.5 dB. Meanwhile, 32-bit float audio can capture the absolutely ludicrous range of up to 1,528 dB. That’s not only massively beyond the scope of 24-bit audio, but it’s beyond the scale of what even counts as a sound on Earth.

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For a bit more scale, a person whispering can be around 20 to 30 dB, while a typical conversation is around 60 dB. A motorcycle driving by would be about 90 dB, and a really loud concert can be in the area of 110 dB. Much higher than this and you’re getting into a range where sound becomes physically painful. If that’s the case, though, why would any recording equipment need to go beyond the 144.5 dB dynamic range of 24-bit audio?

Setting Levels (or Not)

The insane dynamic range of 32-bit float audio is where the claim that you never need to set levels comes from, though even that is a little more complicated than it seems. The highest level a device can record at is referred to as 0 dBFS (the FS here stands for “full scale”). Anything higher than this will be clipped, which is why it sounds distorted when YouTubers scream like that.

Now, typically you’ll set audio levels when setting up your equipment to avoid hitting that limit. Setting those levels involves applying gain to the signal from the mic, which is an irreversible step that crushes the dynamic range of even 24-bit recording.

“When you're recording sound on set, you're usually going to apply gain. And some recorders will apply somewhere between 30 and 90 decibels of gain,” Pereira explains. “That's good when you have a quiet scene where two people are whispering. So you may crank up the dial on the recorder to let's say, plus 60 [decibels]. So now when someone decides to yell, between 60 and 145, that's not a lot of dynamic range.”

With 32-bit float recording, on the other hand, applying gain prior to recording isn’t necessary. “When you're recording in a 32-bit format, there is no volume knob, it essentially just creates a mathematical chart of data that it can then interpolate in postproduction,” Pereira says.

Setting levels on 24-bit systems can be tricky because of the noise floor. To oversimplify, no matter how quiet you make your recording space, there’s always some amount of noise from background objects, or even the electronics you record on. Adding gain to the signal while recording will amplify that noise, as well as your audio source, and once it’s baked into the recording, it’s there for good.

32-bit float recordings have more flexibility to make adjustments after the fact (and in some cases, it might even help with low-level noise problems). That said, it’s important to not let this give filmmakers and sound producers a false sense of security. “It's not going to fix inherent problems of your filming location. For example, if there's an AC or loud fan nearby, recording in 32-bit isn't going to make that noise go away,” Pereira says.

Managing noise on set, and making sure microphones are capturing signal properly will always be important, but once your equipment is set up properly, having the ability to capture audio even past the point of peaking is a useful tool in the belt. But don’t expect to leave 24-bit audio behind forever.

Links in the Chain

So, if 32-bit is so great, why isn’t it the default? For starters, many steps of production–including editing, mixing, and especially distribution–will use a 24-bit workflow, which means that extra data will be lost at some point. And an audio engineer at some stage will need to make adjustments to ensure that the audio signal doesn’t get clipped when downsampling to 24-bit, the same as it would if levels weren’t set properly during the initial recording.

Essentially, this means that the work that would’ve been done initially on set gets offloaded to post-production. So, you have a choice: Either set levels properly on set and record directly in 24-bit, or record in 32-bit and add the extra step later. One way or another, it’s a step you’ll have to do, and some would argue that you may as well do it when you’re on set.

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However, there are some scenarios where having room for error can be a benefit. “Where I do really see 32-bit being a huge advantage is for journalists who are recording out in the field, or for documentary filmmakers that are capturing things that you only get once and can be unpredictable,” Pereira says.

It can also be helpful for indie filmmaker shoots where individuals are doing multiple jobs and there’s not always someone free to monitor levels constantly. Of course, there are other ways to get around this challenge–some recorders, like the Zoom H6, for example, can record a backup track with lower gain to catch audio that peaks. 

There's also the file size issue to consider with 32-bit recordings, though they are a bit overblown. In general, you can expect 32-bit audio to be about 33 percent larger than 24-bit recordings, which isn't nothing, especially if you're recording hours of audio. On the other hand, it's far less than the difference between, say, moving from 1080p to 4K recording.

Like everything else, 32-bit float recording is a tool you can keep in your belt for when you need it. We might not recommend that everyone go out and rush to try a 32-bit recorder like the Zoom F6 ($700) or F3 ($350) immediately. But in some situations, for some productions, it can be helpful to have on hand.

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