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Author Topic: Zoom F6 (32-bit float equipped)  (Read 139919 times)

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Offline jerryfreak

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Re: Zoom F6 (32-bit float equipped)
« Reply #270 on: May 13, 2020, 04:27:48 PM »
first off, thanks, Paul for chiming in on the mixpre - good info as always

back to the zoom:

I decided to do some tests on the zoom, testing recording at 24bit vs 32bit FP at various sound levels, feeding a signal of a properly recorded audience recording from my DAC (Mytek brooklyn, claimed dynamic range of 130 dB)>balanced out>zoom set to mic-in, and adjusted level in 20 dB increments

I knew at extremely low levels i would run into the noise floor of the DAC, so i tried 2 different methods:

1. playing a signal from the computer to the DAC at constant level, and attenuating the DAC output via the stepped pot volume knob (the mytek reads exact dB of attenuation). For this test #1, I used Scott Schneider's most excellent 4015>portico pull from Dick's 9/1/19. it was a 16-bit version (which shouldnt make much difference as any noise would attenuate relative to peak signal)

2. making an file in soundforge that repeated the same 2 minute clip, which i normalized to 0dB (peak), -20 dB, -40 dB, -60 dB, and -80 dB. I then played this back with the mytek set to constant output level. The source material used in this case was an actual 96K 32bit float file i recorded at a concert. After doing the above normalizations, i took the -80dB segment and normalized it back to 0dB. As expected, the 32-bit float container handled the data appropriately and no noise was introduced. That doesnt mean that the -80 dB signal fed to the DAC and then to the zoom is free of noise, but whatever the DAC is putting out should hopefully be recorded by the zoom giving us some vision of the input noise floor and whether recording bitrate affects it. In fact i had to set the volume of the Mytek to -19dB to not overload the zoom in 24 bit mode, so i may have compromised the dynamic range there a bit,so i did test #3...

3. same as #2 above but with mytek 'wide open' at 0dB, i skipped the sample normalized to 0dB, and did -20,-40, -60, -80, and -100 dB samples (the latter of which should roughly correspond to the same ~ -80dB on the zoom as the lowest level sample of test #2)

another variable i encountered was, in mic-in setting, the minimum level the trim in 24-bit mode can be set to is +12dB. so the levels on the iso are 12dB higher. This difference seems to make no difference on signal/noise however

4. same as #2 and #3, except zoom was set to 'line in', and trim was set to -8dB (the minimum) in 24-bit mode. samples normalized to 0, -20,-40, -60, -80, and -100 dB were played back through the mytek set to 0dB volume. The Zoom was input was overloaded a few dB in this case on the 0dB sample. 'Exceeding input volume' was displayed when recording in 32-bit float

5. same as #4, except substituted Tascam DR100 mkiii for the zoom

6. same as #4 except substituted AD2K for the zoom

7. same as #4 except substituted V3 and AD2K for the zoom, and recorded the -60 dB sample with 60 dB of gain on the v3, and then the -80 dB sample with 70 dB of gain on the v3

----------------------------------------------
i normalized volume of all samples with peaks close to zero, then saved as mp3s.

for the case 1 files i went straight across and normalized all of the samples (0, -20, -40, -60, -80)
for case 4, AD2K, and V3 AD2K, i just did -60dB and -80 dB. both the -60 and -80dB samples have a few seconds of (what was) digital silence on the original recording, after each sample

comparing the V3 files to the ones with no gain, it was apparent i was running into the noise floor of the DAC.

That said, all the files sound darn near *identical* to me, and the noise floor in between samples is basically identical on both the 24 and 32 bit samples. the -60 dB samples are passable in both cases, the -80 dB samples are excessively noisy

on hot signals the zoom overloaded at the exact same points (even though with the trim, the 24 bit files were hotter. the 32 bit files had lower level but the same harsh clipping

Im not sure how valid the test was, due to the inherent noise floor from the DA. I think i need to do another test with the lowest sens mic i can manage. perhaps a DPA 4006A or 4007A with the 20 dB pad on. Which do you think would be more useful, the 9mV/Pa 4007 with the 24 dBA noise floor, or the 40 mV/Pa 4006 with a 15dBA noise floor. Both those specs are before the 20 dB pad.

what other gear would allow me to run a clean-ish low level signal in? maybe come off the mytek with a hotter signal and use some XLR inline pads?

in any case, it seems that for all *practical* purposes (i.e. guessing recording level within 40, or heck even as much as 60 dB), the 32 bit doesnt offer additional resolution

files for your listening displeasure. Even though they are mp3s it might be best to open them up in a wave editor so you can get a visual for the samples at which you are looking
https://drive.google.com/open?id=1taG_IOlFEnlXZsD0bmveKt6XWLYmefAa
« Last Edit: May 13, 2020, 06:30:26 PM by jerryfreak »
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Offline jerryfreak

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Re: Zoom F6 (32-bit float equipped)
« Reply #271 on: May 13, 2020, 04:28:46 PM »
It's worth noting that the F6 allows phantom powering while the inputs are set to LINE, and in that mode they can handle an input level of +24 dBu.  I haven't tested it myself, but I imagine that a pad is being inserted in that mode

confirmed by zoom support
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Re: Zoom F6 (32-bit float equipped)
« Reply #272 on: May 13, 2020, 06:48:23 PM »
Jerryfreak, Big thanks for the tests you've made and posted about above.  That further bolsters my previous conclusions about minimal advantage of switching from recording at 24/48 with regards to my scenarios, the value of practicality and diminishing returns.

If set to Reference Level, the track knobs are faders for the L/R downmix.  I never use the downmix, so I prefer setting to Rec Level, which actually changes the levels of the 6 ISO tracks being written to the card, post-ADC.  So even though the gain is fixed, you can set to Rec Level and crank the hell out of your channels so you have ridiculously high (or low) levels being written to the files. In Rec Level mode, the downmix faders are bypassed, but I still consider the knobs to be faders because their level adjustment is happening well after the input trim (again, which is fixed in this mode).  See pp. 194 and 198 in the manual which show how this works.

Thanks for explaining this, as it would apply to my currently preferred method of managing the relative balance between ISO channels when recording to an F8.  BTW, before going further, I fully recognize that what I am about to describe is not applicable to the working methods of most tapers.  Feel free to ignore..

As you are probably aware, I'm typically using F8 to record an 8 channel OMT multi-microphone array which consists of various spaced mics and a center Mid/Side pair, a configuration which does not vary appreciably at this point.  Partly because it helps with setting up rough playback mixes on recorder itself, I've found find it helpful to set recording levels so as to achieve an approximately correct relative balance of levels across closely-related microphone pairs and groups that make up the array.  This wouldn't matter (as much) if I were simply dumping the ISO files to the computer and doing all the mixing there.

As discussed in other threads, M/S playback decoding on the F8 is not as robustly implemented as I would prefer.  This will not affect most tapers except those making live 2ch mixdowns on the machine or using internal mixing for "ride-home listening".  If Mid and Side channels are recorded directly as ISO tracks rather than as an L/R pair, playback decoding to L/R can be switched on for the pair, however doing so eliminates the possibility of adjustment of M/S ratio and adjustment of level of those channels in the mix.  Instead, the ratio and level of the pair are determined by the input trim settings for those channels as recorded.  Other ISO channels which do not require M/S decoding can be panned and level adjusted, so I go about building a rough 2-ch mix in the recorder by starting with the 'defacto locked' M/S pair and add the other channel groups to that.  Not ideal but makes for a acceptable work around.  At the very least, this requires setting a close enough to correct relative ratio of Mid and Side trim levels when recording.  In reality, it helps to have most of the channels recorded close to the correct relative mix level in relation to each other, and not simply each pair balanced in relation to itself, or all channels set individually for optimal peak headroom.

The functionality you describe above would allow me to continue doing working in this way (if necessary) on a 32bitFP successor to the F8N, assuming such a recorder would operate similarly to F6. Hopefully M/S playback decoding in a successor Zoom recorder will be better implemented, avoiding this issue.

I'm mostly just thinking out loud here, clarifying for myself the potential path forward from F8 to perhaps SD MP10 mkII or its successor, a Zoom F8N successor, or some other yet to be realized 8 preamp recorder.  Although I prefer some of the Zoom features (8 standard XLR inputs, writing mono or stereo files, simpler navigation) the SD remix/re-record feature Paul mentions is very attractive for my unusual way of rough-mixing within the recorder away from a computer.
« Last Edit: May 13, 2020, 06:50:44 PM by Gutbucket »
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Re: Zoom F6 (32-bit float equipped)
« Reply #273 on: May 13, 2020, 07:41:53 PM »
It's worth noting that the F6 allows phantom powering while the inputs are set to LINE, and in that mode they can handle an input level of +24 dBu.  I haven't tested it myself, but I imagine that a pad is being inserted in that mode

confirmed by zoom support

Thanks.  So does that mean for practical purposes, the F6 can handle mic signals of +24 dBu as long as the input is set to Line?  Then the next question of course is what impact inserting this pad would have on sound quality.
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Re: Zoom F6 (32-bit float equipped)
« Reply #274 on: May 13, 2020, 08:50:54 PM »
yes, it can do +24dB with phantom

per my tests it definitely raises noise floor.

I personally wouldnt expect to go over +4dBU with mics and would avoid using it, but we have discussed some very sensitive mics in this thread so YMMV

clipping the input sounds very bad... I haven't investigated use of limiter or where it is in block diagram, but perhaps mic-in+limiter could be preferable to line-in, as it would affect *some* sample data as opposed to raising noise floor at all times
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Re: Zoom F6 (32-bit float equipped)
« Reply #275 on: May 14, 2020, 12:46:28 PM »
^ This was the basis of my decision to stick with the F8 rather than move to F8N.  The primary question was to continue using F8 with the advanced limiter switched on for safety, or switch to F8N because it can provide phantom power in line-input mode.  I rarely engaged limiters on any of my previous recorders and prefer not to use them when possible, but my tests with F8's advance limiter convinced me that in my recording scenarios its use was acceptably transparent. However, what I've not tested nor determined clearly is if switching on advanced limiter increases noise-floor by the same amount as switching from mic to line-input.  I suspect it does, a consequence of both modes using the same input pad prior to ADC.  If that is indeed the case, my better choice would be line-in to F8N, achieving the same noise-floor without any need to engage limiting.

My apologies for my F8 related posts in this F6 thread. I consider them relevant because with the exception of channel count and absence of 32bitFP recording mode, F8N is essentially the same as F6 in these ways.
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Re: Zoom F6 (32-bit float equipped)
« Reply #276 on: May 14, 2020, 02:11:16 PM »
What am I not understanding?

With a 24bit recorder, I have to think about setting levels (a little bit.) If I set them too high (say +25db for a FOB show), I might get overs.

With a 32bit recorder, I don't have this issue. I don't even need to unzip my bag and can start and stop the recording with the app? 
Recording:
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Re: Zoom F6 (32-bit float equipped)
« Reply #277 on: May 14, 2020, 03:43:29 PM »
That's the basic gist of the differences with regards to making a taper recording.  I was unclear WRT understanding all differences between the two after the recording has been made, which is a different aspect yet was cleared up somewhat by voltronic and jerryfreak.

Concerning my somewhat OT aside above about the manipulation of signal level prior to writing the file as a way of achieving a closer relative level balance between channels, that is really just a practical "nice to have" thing rather than a necessity.  Ignoring that, I typically use the 24bit F8 in the same way that you describe use of a 32bit recorder.  I just turn it on and press record.. to the extent that I would have used the app to do exactly as you mention with a zipped bag last fall when I considered putting the entire rig up in the rafters prior to a show, except I had no Apple device to host the Zoom remote app.

Those things represent the important practical take-aways for me.  The other stuff is more arcane, confirming noisefloor performance and understanding how everything is actually working.
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Offline jerryfreak

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Re: Zoom F6 (32-bit float equipped)
« Reply #278 on: May 14, 2020, 04:04:30 PM »
What am I not understanding?

With a 24bit recorder, I have to think about setting levels (a little bit.) If I set them too high (say +25db for a FOB show), I might get overs.

With a 32bit recorder, I don't have this issue. I don't even need to unzip my bag and can start and stop the recording with the app?
it would be more like recording at +0dB in the former case to the same end result. assuming both recorders are equally remote capable

(as an aside, zoom remote app blows the sound devices out of the water in functionality btw. controls nearly every aspect of the recorder.)
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Re: Zoom F6 (32-bit float equipped)
« Reply #279 on: May 14, 2020, 07:01:19 PM »
What am I not understanding?

With a 24bit recorder, I have to think about setting levels (a little bit.) If I set them too high (say +25db for a FOB show), I might get overs.

With a 32bit recorder, I don't have this issue. I don't even need to unzip my bag and can start and stop the recording with the app?
it would be more like recording at +0dB in the former case to the same end result. assuming both recorders are equally remote capable

(as an aside, zoom remote app blows the sound devices out of the water in functionality btw. controls nearly every aspect of the recorder.)

It sure would be nice to have an Android version.  I would use it for all of the rehearsals and concerts I record where I am on stage performing, saving a lot of file size.  As it is now, I start recording 30-45 min before concert time because that's usually the last chance I have to get at my rig.
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Offline jerryfreak

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Re: Zoom F6 (32-bit float equipped)
« Reply #280 on: May 14, 2020, 11:22:38 PM »
fortunately refurbed iphone SEs can be had for $60 or so. i paid more than half of that just for the bluetooth dongle for my zoom
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Re: Zoom F6 (32-bit float equipped)
« Reply #281 on: May 15, 2020, 08:55:14 AM »
ok i did some low level tests with actual microphones

record rig:
channel 1 (low sens mic) DPA 4018VL+MMP-A body with 20 dB pad engaged on mic body
channel 2 (high sens mic) DPA 4006 (old style w/ integrated capsule)
into zoom F6 on a stand

playback rig:
sony A10> full volume > sennheiser HD600 around my neck standing about 30" from mics
source material: "Deep Into the Night" by Hiromi Uehara's Sonicbloom
my best guess on my SPL calibrator is the volume of the music at the mics was peaking at about 60-65 dB (like absolute dB volume in the air, not dBU levels on recorder)

'trim' was set to +12 dB in 24 bit case, and of course is disabled in 32 bit case

24 bit data was volume adjusted by L +103dB   R +43dB
32 bit data was volume adjusted by L +85dB     R +67dB

i have no idea why the relative channel levels were so different between the two tests. maybe i messed with the trim on one of them. in any case they are both *very* low level tests with the same source material volume

stats on wavs before volume adjustment
24 bit test
                                                    Left Channel           Right Channel       
Minimum sample value (dB)                           -103.205               -43.151             
Maximum sample value (dB)                           -103.510               -40.875             
RMS level (dB)                                      -124.494               -65.758             

32 bit
                                                    Left Channel           Right Channel       
Minimum sample value (dB)                           -83.561                -65.768                     
Maximum sample value (dB)                           -83.768                -65.122             
RMS level (dB)                                      -106.416               -91.226             

added to the shared folder linked above as 'atest.mp3' and 'btest.mp3'
those are the files with different mics on each channel (warning: the low sens mic on the left channel is pretty noisy on both samples

i made additional files by swapping the 4006 to both channels, so each of 'ctest.mp3' and 'dtest.mp3' are dual mono recordings of the 4006 (one is 24 bit, one is 32 bit)

can you guess which is which?

I only have one 4006 but if theres interest maybe ill repeat the test with a pair of 2006, 4011, or 4007 without mic pads and double check the trim next time



« Last Edit: May 15, 2020, 09:19:43 AM by jerryfreak »
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Re: Zoom F6 (32-bit float equipped)
« Reply #282 on: May 15, 2020, 09:45:59 AM »
Jerry,

Thanks for doing these tests.  I am listening with the L/R tracks split and soloing to hear one mic at a time.  I ignored the 4018 tracks with their much higher noise, and focused on the 4006 tracks.  I certainly cannot tell which are the 24-bit and which are 32-bit FP.  The only conclusion I can draw is that at levels this low, you are amplifying the mic self-noise and preamp noise so dramatically that any benefits of 32-bit FP disappear.

I would suggest repeating the test but recording the output of speakers rather than headphones, and using a more realistic "too low" level.  Maybe set it so the input levels on the F6 are peaking at -40 dB.
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Re: Zoom F6 (32-bit float equipped)
« Reply #283 on: May 15, 2020, 09:59:40 AM »
i was concerned that speakers played at very low volume might have a lower S/N than open cans played at full volume, but i can try miking a single BM5A with the 4006. it’s the quietest mic i’ve got, i believe

that room i did the test in had NOTHING plugged in i was trying to get background noise as low as possible. i wanted to test outside but alas it was raining. with tinnitus i’m not the best judge of quiet spaces


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Re: Zoom F6 (32-bit float equipped)
« Reply #284 on: May 15, 2020, 10:36:14 AM »
Disclaimer- I'm not listening thru a high resolution playback chain, simply using Samsung phone in-ears straight out of computer. dtest sounds brighter to me than ctest, although relative S/N ratios seems about the same WRT both noise spectrum and signal.  Note stomach or dog growl at 2:00 in atest!


I also wish for an Android version of Zoom remote app.  Have considered picking up the iphone SE just to run this app, but have not been recording enough, especially in situations where it would really be advantageous rather than simply fun.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

 

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