Comment by nok22kon
4 days ago
Rode NT1-A 5th gen microphone claims 32-bit float output, insisting it will not clip peaks
so maybe they do sample at 24 bit at a well chosen gain level and then convert to 32 bit float, with the max 24 bit value being above 1.0 float
or as GP said, use two separate ADCs at two different gains and combine their output
> Rode NT1-A 5th gen microphone claims 32-bit float output, insisting it will not clip peaks
Of course it does! And that's what it does, of course. But that has absolutely nothing to do with the AD process itself, which is chip-limited to 24 bits and likely physics-limited to somewhat less than that.
You can't beat the physical limit of a DA circuit by doubling them up at different gains.
And .. you don't want to. Going beyond 22 bits gets you into brownian noise pretty quickly, which is completely pointless.
The best you can do (or could do) is get a very, very, very good DA that can really do 22 bits (likely not commercially available because of the expense), and then get the samples from it in whatever format works best for your purpose (24 bit integer, some fixed point value, or 32 bit floating point).
you have 22 bits for the typical audio voltage level, which you call 1.0 float
but what if you "allow" double that voltage and call it 2.0 float? a strong pressure into the microphone generates a stronger voltage
thermal noise limits you on the quiet signals, but not on the powerfull ones
so 22 bit for typical -1.0 -> 1.0 range and you can add a few more bits on top of that for stronger audio pressures (voltages) which you would traditionally clip
Sorry, but this not how AD works. If your idea was valid, we'd have new generations of ADCs in our hands.
7 replies →
> use two separate ADCs at two different gains and combine their output
That's what could be done if ADCs were perfectly linear and noise free and limited only by their bit-width. Sadly, they are not. The non-linearity one can in theory measure and correct for, but the noise can be corrected for only by oversampling. And then you might as well use a single ADC of lesser bit width and higher sampling rate.
I feel like you’re arguing against a straw man.
No one is arguing that there are practical audio microphones + ADCs that produce accurate, undistorted 32-bit float output across the full representable range. But they don’t need to! For professional use, the ability to produce perceptually accurate output, with inaudible noise, across a very wide dynamic range, is extremely useful. Think of it as fancy, real-time AGC. It does not need to be perfect. If you can record a loud transient without substantial distortion, and also record sounds with 2^16-fold lower amplitude (~96dB lower) while still remaining well above the noise floor immediately after the transient is gone, this ability is useful. Plenty of real-world noises are well above 120dB, and plenty of human-audible sounds are below 20dB. You can’t play back the recording, at least not without making parts inaudible or injuring your audience, but you can edit it. And a setup like this lets you do it with one microphone and no fiddling with gains in advance.
this uses 2 ADCs:
https://tascam.jp/int/feature/32-bit_float
One cannot create a noise-free, perfectly linear 32b ADC using 2 lesser ADCs as described above. That is however not needed and I suspect isn't what they are attempting.
If, say, two 24b ADC (20b noise free, non-linearity 2LSB) with one receiving the input signal with an approximate 10bit higher gain (+60dB) and one would combine their outputs with that 10b shift (and ignoring the input of the low gain path, if the signal falls below a given threshold to reduce the noise contribution of that ADC and the input of the high gain path if the signal exceeds another threshold in order to avoid clipping), then one could construct a 32b float.
This doesn't improve resolution (which arguably would be pointless) or linearity (not all that critical in audio methinks) but dynamic range, which I can see some appeal of (in extreme recording situations, say you'd want to record the breathing of a shooter followed by the gun shot -- there remains the challenge of finding a microphone capable of a 120dB range, but perhaps one could use two different ones ...).