Topic: Zoom F6 (32-bit float equipped)

[carpa]

Given that part of this discussion is related to the mic input’s capability with the risk of overload due to a hot signal, it is interesting to observe that f6 and f4 don’t share the same specs. They both feature mic mode and line in mode ( padded) but while in mic mode f6 can hold +4 dB, f4 accepts up to 14db ( from the user’s manual). Seems a bit strange given that the automatic gain setting in 32 bit mode would seem to get the best benefit from a safer spec.

[jerryfreak]

they spec the +14dB with limiter *on* , in both F4 and F8. i wonder if thats the difference?

manual says "The F uses a newly-designed limiter. This limiter has 10dB of
headroom, preventing distortion and allowing it to keep signals
below the set threshold even more than ordinary limiters."

that 10 dB cant merely be a coincidence....

i might try to feed the F6 a +14dB signal with a limiter and see if it takes it in both 24 and 32-bit mode

F8n also specifies +14dB input,but looking at the F8n manual, the limiter is more similar to the F6 (menu is identical), vs the F4, which doesnt have the "advanced" mode

[jerryfreak]

confirmed by zoom support:

Zoom: the F6 preamps were re-designed compared to the F8/F8n. The F8 and F8n have the same preamps.  (on the F6) The preamp gain is analog, but the Trim on the F6 acts as a digital stage.

me: so is the analog preamp stage fixed gain? and then digitally attenuated by the trim?

Zoom:Yes, the analog stage is fixed. Digital attenuation is adjusted by the trim.

we had other discussion about 24-bit vs 32-bit, im going to hold off on posting that until theres some thoughts on the sound samples i posted, so as not to color the opinions

[carpa]

@jerryfreak  So, according to Zoom's staff answer, the  preamp design between F4 and F6 is different, probably slightly; still could be possible that the difference in mic input's spec ( +4 db max for F6 and +14 for F4/8) comes from the design more than referring ton on/off pad?   I would make not much sense, though, to have less flexibility on a fixed gain than on a variable one.

[jerryfreak]

@jerryfreak  So, according to Zoom's staff answer, the  preamp design between F4 and F6 is different, probably slightly; still could be possible that the difference in mic input's spec ( +4 db max for F6 and +14 for F4/8) comes from the design more than referring ton on/off pad?   I would make not much sense, though, to have less flexibility on a fixed gain than on a variable one.

both designs have pads. i'm not sure i really understand your question, in any case I dont think I know enough about the gain stages of either unit to answer it.

[voltronic]

@jerryfreak  So, according to Zoom's staff answer, the  preamp design between F4 and F6 is different, probably slightly; still could be possible that the difference in mic input's spec ( +4 db max for F6 and +14 for F4/8) comes from the design more than referring ton on/off pad?   I would make not much sense, though, to have less flexibility on a fixed gain than on a variable one.

both designs have pads. i'm not sure i really understand your question, in any case I dont think I know enough about the gain stages of either unit to answer it.

The max input on the F6 set to LINE is +14 dB, so there's your 10 dB pad.  On the F6, you can use LINE+PHANTOM so if you have a mega-hot signal from your mics coming in, you can use that setting.

[jerryfreak]

The max input on the F6 set to LINE is +14 dB, so there's your 10 dB pad.  On the F6, you can use LINE+PHANTOM so if you have a mega-hot signal from your mics coming in, you can use that setting.

its +4/+24 on the F6 when the 20 dB pad is engaged

[carpa]

The max input on the F6 set to LINE is +14 dB, so there's your 10 dB pad.  On the F6, you can use LINE+PHANTOM so if you have a mega-hot signal from your mics coming in, you can use that setting.

its +4/+24 on the F6 when the 20 dB pad is engaged

That's what I meant; it seems that F4, both with or without pad, can accept a hotter signal

[jerryfreak]

with a limiter

its not apples to apples.....

[voltronic]

The max input on the F6 set to LINE is +14 dB, so there's your 10 dB pad.  On the F6, you can use LINE+PHANTOM so if you have a mega-hot signal from your mics coming in, you can use that setting.

its +4/+24 on the F6 when the 20 dB pad is engaged

Whoops sorry I had my specs mixed up with SD MixPre-II.

[jerryfreak]

no takers on the noise floor tests, huh?

[Gutbucket]

I gave a listen out of curiosity when you posted the link. My overall take away as recall: a couple are obviously noisier (well-duh) 

Going back now and listening again to comment. Disclaimer- I'm listening via web-preview feature, using cheap Samsung earphones, but at least without cotton in my ears.

Impressions:
1) Too many files to expect folks to really listen and compare closely I think.  Not sure of the blind test value because of that, maybe better to know which is which while listening even with the bias that imposes.
2) d and e are really noisy.
3) The noise spectrum differs very slightly but is pretty close to the same level for all other samples.  Could live with any of those and put any concerns about minutia to rest.
3a) .. but not sure that in real world use even noisy d and e would represent a problem.
4) Right channel signal is hotter (equating to lower noise after equal level adjustment of signal) but is less clean. I prefer the Left channel signal.

No analysis done other than listening.

[jerryfreak]

4) Right channel signal is hotter (equating to lower noise after equal level adjustment of signal) but is less clean. I prefer the Left channel signal.
.

yes they were different mics (one dpa and one schoeps). the fact that you can hear differences in noise character between them indicates the mic self noise is at least as apparent as the input noise floor.

as for the two noisier samples...... that was with the line-in setting, as i mentioned before using line-in indeed raises the noise floor considerably, there is no free lunch when it comes to dynamic range.

[jerryfreak]

some questions zoom has answered for me in last week or so

The dual ADC is used when recording in 32 bit float and when recording in 24 bit. The Trim allows you to set the level that will be recorded to the 24 bit file. This makes it so that if the signal clips in 24 bit mode, it is due to the file clipping from the limitations of the 24 bit integer format, not from clipping at the converter. Since linear formats cannot accommodate the wide dynamic range of the dual ADC on the F6, a software Trim is necessary to set the level of the recorded file.

in terms of what you wrote i'm not sure i understand the difference between clipping because of integer file format vs clipping the converter. wouldn't both fundamentally describe going over FSD (unless you're talking about overloading the analog front end of the converter)

Yes, we are referring to overloading the analog front end.

i've done some tests recording relatively quiet source material , both line in, and mic in, and i really can't hear a difference in the integer vs float files when normalized. it seems like the EIN is the limiting factor.

As you point out here, the theoretical implications of 32-bit float are limited by hardware. With a quiet signal, I wouldn't expect you to hear a difference in the integer vs float files.

considering that in either integer or float the max input level is +4dbu, and the EIN is fixed, i don't quite understand how the float files increase dynamic range between these two endpoints. i understand how the two ADCs can have a wider range of 200 db or more, but i still can't wrap my head around how that increases the 120ish db dynamic range of the input

The preamp and ADC are going to act the same whether in float or integer. Floating point allows the final recorded file to have an extended dynamic range. So if recording in integer, the bit depth itself will limit the dynamic range meaning that somewhere in the full dynamic range of the preamps and ADC's it will have to cut it, meaning there is a ceiling and a floor which will either clip or not record. When recording float files, you can capture the entire dynamic range possible.

one more question: since the trim is acting as an attenuator, when recording in 24-bit mode would the best performance be achieved with trim set to 0dB?

Not necessarily. Because both AD converters are working all the time, where the trim is set doesn't have as much effect on the performance as what the AD converters decide to do 

...or set to its maximum? would the latter be adding additional digital gain?. What trim setting would be considered 'unity gain' in 24 bit? 0dB isnt available as a setting in mic-in, of course

The trim adjustment is really just setting where within the available dynamic range you want to capture. The usual rules of setting gain in 24-bit should be followed because you still want to capture loud enough signal that it is high quality.

im assuming in 32 bit float, (where the trim is disabled), that the input range is already optimally matched to the input of the ADC

Correct

[jerryfreak]

so that said, apart from some (measurable but perhaps not audible) bit utility on the bottom end, the only practical advantage 32 bit offers is in regard to setting levels too high, which is easily remedied by reducing recording level in 24-bit mode

if you overload the input (same levels in either case), the results will be the same

functionally speaking, when in 32-bit mode the zoom will at least give you the 'exceeding input level' warning which it doesnt give in 24-bit mode