Over/Under in 32-Bit Float

The MixPre II recorders includes a new 32-bit float recording mode. To an experienced audio person, the promise of this “gain independent” type of recording seems too good to be true. For years, we’ve all been trained to set the gain high enough to get over the noise floor of the A-to-D converter (or the recording tape!), but not to set the gain so high that the sound saturates or clips. 

With 32-bit float recording on the MixPre II series, it really doesn’t matter where the gain (trim or fader) is set. The incoming audio gets scaled up or down within the recorded file with its full dynamic range. Since the A-to-D converter has 142 dB of dynamic range, and the 32-bit float file has hundreds of dB of dynamic range, the MixPre II is practically only limited by the dynamic range of the microphone itself. Seeing (or listening) is believing though.

We recorded an acoustic guitar using an AKG C414 mic. We then split this passively into channels 1, 2, and 3 of a MixPre-10 II, using 32-bit float recording. We recorded this “poorly”, intentionally setting the channel 2 and 3 gains incorrectly. The channel trims were set like this:

1. 46 dB (good gain setting for this recording).
2. 6 dB (40 dB too low)
3. 76 dB (30 dB too high)

Here’s what the resultant file looks like when viewed in iZotope RX7. Notice, as expected, channel 2’s audio is way too low, and channel 3’s audio is way too hot and everything is clipping.

We then took this WAV file into Reaper and applied +40 dB of gain to track 2, and applied -30 dB of gain to track 3, and also split these into separate files. All three of these files end up sounding identical. Here is what each of these files looks like with iZotope:

Track 1 (0 dB applied)

Track 2 (+40 dB applied)

Track 3 (-30 dB applied)

As you can see and hear, the original audio is perfectly captured no matter where the gain on the recorder is set. This can make recording a bit less worrisome in some circumstances as the level of the audio can be adjusted after the fact in the DAW without losing any fidelity of the original signal.

It is worth noting that this 32-bit float is an optional setting on the MixPre II series, and that the MixPre can be operated also just as a standard 16- or 24-bit recorder making standard WAV files. Have fun using this new mode, and happy recording!