Zoom have just announced a new 'Pro' version of their popular F8n field recorder. The F8n Pro is functionally the same as its predecessor, but with two major enhancements: first, its maximum SD card capacity has doubled, to 1TB per card (it features twin SD card slots), and secondly, it's capable of recording at 32-bit floating point.
The 32-bit capture development is significant, as it essentially eliminates the need to worry about gain staging and clipping while recording. As SOS Technical Editor Hugh Robjohns explained in a recent SOS Forum post:
Most microphones can deliver a usable dynamic range of 130dB or more. The very best 24-bit A-D converters can manage a dynamic range of maybe 122dB, and the less expensive ones are more like 115dB... and the analogue electronics of the preamps may well have less dynamic range than that.
So what Zoom have done is split the input signal to feed two preamps, each feeding its own A-D converter, with each set optimised to handle a different segment of the total audio dynamic range from the source.
So in the simplest form, one preamp/A-D looks after the quieter sounds, and a second preamp/A-D takes the louder sounds. A DSP chip receives the outputs from the two converters and decides when to use the data from each on a sample-by-sample basis, effectively splicing them together to make a single converter with a much larger dynamic range than each individual element. The selected data is then slotted into a 32-bit floating point format with the appropriate amplitude scaling data which is what is recorded.
A perfect 24 bit system has a theoretical dynamic range of 141dB (it's often quoted as 144dB, but that's without dither, which isn't a good idea...). However, the very best 24-bit converters are struggling to achieve more than about 122dB in practice at the moment. This multi-preamp/converter technique gets much closer to achieving a realistic 140dB-ish dynamic range capability in the converted signal.
It's also worth remembering that 32-bit floating point uses a 24-bit mantissa, so the source audio sample's dynamic range can't be more than 140dB or so, but that chunk of 'high-resolution' audio can be scaled up or down within a 1500dB dynamic range window, which is handy when it comes to post-production.
So these 32-bit floating-point recorders can now capture the full dynamic range output from the mic at both extremes of its range — the quietest parts are handled by the low-level preamp, which is optimised for low noise without having to worry about headroom, while the loudest parts are handled by a preamp optimised for headroom without having to worry about low noise.
The result is the best of all worlds, where the preamp is no longer the weakest link in a wide dynamic range signal chain, the converters don't have to be the best on the planet yet can deliver phenomenal dynamic range, and the operator no longer has to determine the preamp gain manually in an effort to optimise the signal level in relation to both the headroom and noise-floor.
A very worthwhile improvement, then, made all the more practical by the increased maximum SD card capacity (32-bit floating-point recording uses more data than a traditional fixed-point data stream).
The Zoom F8n Pro is due to go on sale later this Spring, and is priced at £1122 including VAT. To find out more about its features, check out Hugh's review of the original here.
