Why the Zoom F4 does not work as an ENG field mixer, feeding line level into a camera

B

bengiles

Well-known member
I thought this might be useful for those who may be considering the purchase of an F4 - it collects together some of my findings and discoveries that have been spread across various threads and websites. Thanks to Jens Mathias on Facebook for working with me to get the answer. I don't mean for it to put anyone off buying an F4 - but just to clarify what seems to me to be an important design flaw that may or may not bother you.

Firstly, I really like the F4 - but it doesn't work as a field mixer that feeds analogue line level into a professional camera. There will be some people that are using it as such, but read on and I'll try and explain as briefly as I can why it's a flawed approach.

The F4 is a digital unit, feeding a DAC with analogue XLR outputs. Most people (me included) will interpret that physical XLR spec as "professional line-level +4dBU balanced outputs."

But they're not. They're -10 dBV domestic line level outputs, the same level you normally get on, say, a CD player with RCA outputs, masquerading as professional XLR outputs.

So, if you try and line up the mixer at unity gain to a professional camera XLR line in, you'll end up cranking the camera input pre-amps right up to 10.

I've read various comments saying, "just push the F4 master output gain up." I did, and various listening tests suggested it was a workable solution - but only because I was letting things peak on the F4 around -12 dBFS.

Have a look at the recorded waveform on the camera files, and you'll see that all this actually achieves is bringing the clipping ceiling down. In other words, you can crank the digital gain higher, but the DAC is natively designed to output at -10dBV. Think of it like a guitar fuzz pedal - you're cranking the gain up, but it's ultimately restricted by the final output stage, and the result is distortion/clipping.

The waveform I created below demonstrates the effect of cranking up the F4 master output to +12dBFS, and bringing the camera preamps down to calibrate unity gain. Channel 1 was set to allow signal peaking just under -12 on the F4 meters. Channel 2 was allowed to go hotter, peaking higher up around -3 on the F4 meters. The result? Anything that went above -12dBFS on the F4 meters is horribly clipped/compressed on the camera at -12dBFS, losing you a fat chunk of dynamic range. Look at it below, and you'll see what I mean.

Waveform 3.jpg

So what's the solution? In my case, I've accepted that it's not a line level mixer. I use a Tentacle Sync on my FS7 and feed timecode from the F4 at the beginning of the day. I then take a radio hop of the F4 master outputs into the FS7, for monitoring and guide purposes. Tentacle Sync Studio then very effectively syncs it all up afterwards and re-wraps the MXFs as MOVs, keeping the essence intact, ditching the audio timecode and adding in all of the F4 recorded tracks.

One other potential option is to reduce the F4 master outs and treat them as a "hot mic" output, feeding mic level to your camera. I haven't tested that option - but only because I'm not a fan of feeding mic level from a mixer to camera, and freeing up my sound recordist partner with a radio hop has other benefits.

Either way, bear in mind that the F4 slate tone is post fader - so it's independent of the master out level. If you want to reduce the master out level to hot mic, you'll need to record some tone (you can set the level in the slate tone menu at -20 or -18 for example) and play that back, so you can calibrate for unity gain.

I hope this is helpful - it's not meant in any kind of trolling way. I love the F4, and what it offers at the price point, but hopefully this might be useful feedback to Zoom for their next iteration - and if there's anything they can do about that output DAC (I suspect not, as it looks to be hardware limited), that would be utterly fab. I'm happy to edit this post, in light of any developments/workarounds.

Ben.
 
Well, that seems to settle that.

I wonder where I got the idea that the output was +4? Probably from some of the adverteasing when it came out. I ordered mine the next day after it was available. Luckily, if I ignore the slate tone, I get a signal into my old camcorders that works just fine. Easily records at -12 which is just where I want it. But then I ain't a pro, who has people down line expecting -3.
 
VERY nice job here on explaining this. I've been messing around with the F4 a lot lately, and I'm very impressed at what this little machine can do for the cost, but as you say, it isn't a mixer. I'd be surprised if the design team of the F4 were thinking of it as a mixer, to be honest with you. That being said, if those main outs were actual line level, then this would be a different story.

I mean...I guess you can mix internally on the machine, and that's a good thing. In terms of double system audio, it's great. What you are doing with your wireless feed to camera is exactly what I'd be doing as well.

My two suggestions would be to make those outputs actual line level and allow me to route any input to any record track that I want. I want to put a mono mix on track one, and as it stands I can't do that. Putting the mono mix on track one is kind of the industry standard these days, and picture editors are used to that, and when they don't see that they can get confused. Yeah, they can just look at the sound report to see track assignments (because you should be doing a sound report), but most of the time it gets ignored, but at least when you do one you've covered your @$$ and can say "did you look at the sound report?".

But other than that, this is a great machine at a price that is very agreeable. I have it in my bag with some wireless and power distribution and it does the job well for what I need.
 
Great post. It won't stop me from buying one but it is kind of silly to have -10 output on XLR. Nothing I know of with an XLR input is going to be expecting -10.
I suspect it is growing pains of a dedicatedly consumer product company stepping into the professional/ prosumer market and will be fixed in a later generation.

I also doubt that it can be fixed with a firmware update but? The DAC may have a setting?
 
The F4 and F8 were designed more for multi-track recording than mixing, though Zoom has an external linear fader option available, but that's more for a cart-based set-up and does not solve the output operating level issue. I agree the lack of a nominal +4 output is a bummer. This was discovered soon after the F8's initial release and I don't if it's fixable via a firmware rewrite. May be hardware related and not fixable. Otherwise most folks concur the F8 and F4 are decent. I only got to play around with an F8 at an AES trade show.
 
OH...another thing I'd like to see changed is that it'd be nice if the media slot were on the side or the front. It's hard to get to when it's on the bottom and the F4 is in a bag. I have my F4 in a Stingray Junior bag, and the bottom of the bag has a trap door that I can open, but it's still a drag. It'd be much easier to just reach in the side blindly and grab it.
 
The output of gear has changed over the years. 30+ years ago the pro standard was +8, then it was changed to +4 my mixer manufactures in Japan, the reason why is it better suited the IC electronic revolution.
By lowering the output level less power is used so for the F4 / F8 Zoom may have done this to improve overall battery life of the unit.

When I bought my F4 i was very aware of the level out being -10 and not +4. This is not a big thing for me and at times setting the output level to mic level may be an advantage when using plug in Tx units.

I have also noticed people are getting confused with the SIGNAL reference tone level of the unit, it is -20 in a 0>-100 scale and actually quite different from the actual OUTPUT level of the unit being -40 (mic level) -10 (what the Zooms are which is prosumer level) and +4 (which is Pro level)
 
Well, if one is desperate, they do make such a thing as a line-level converter that will boost -10db to +4db. Full Compass lists a bunch of them on their site.
 
Noiz2 said:
Great post. It won't stop me from buying one but it is kind of silly to have -10 output on XLR. Nothing I know of with an XLR input is going to be expecting -10.
I suspect it is growing pains of a dedicatedly consumer product company stepping into the professional/ prosumer market and will be fixed in a later generation.

I also doubt that it can be fixed with a firmware update but? The DAC may have a setting?
Click to expand...

Strangely enough, the Amira seems to take consumer line level on XLR. At least it did the last time I worked with one.
 
OzGizmo said:
I have also noticed people are getting confused with the SIGNAL reference tone level of the unit, it is -20 in a 0>-100 scale and actually quite different from the actual OUTPUT level of the unit being -40 (mic level) -10 (what the Zooms are which is prosumer level) and +4 (which is Pro level)
Click to expand...

You are getting confused yourself. Line level the -10 & +4 is measured in dbu. The reference tone in the F4 is measured in dbFS (I think): -20dbFS is = to 0 dbVU, which is equal to +4 dbu. Me? I am really confused about dbFS as I find conflicting information out there (-12dbFS should also be 0 dbVU in 16 bit, as opposed to 24 bit; but some say it is, and some say it ain't). I finally decided that I would just go with what worked for me digital wise, and ignore the theory stuff. I do understand the analog side quite well, a lot of folks do not understand that side either.

However, you may be correct about the "Slate Tone" using a purely arbitary level scale. You may note that Zoom does not call it a "calibration tone" or a "reference tone". That would make it a real problem trying to use it that way.

I wonder if anyone has tried feeding a calibrated tone through the F4 to set everything up. Unfortunately, my analog microphone mixer only has +4db output, so I could not feed a 0 dbVU reference tone into the F4 with it.

Which leads to a new thought: What if I used the portable mixer to set the levels on the mixer deck connected to the computer. Then connected the F4 to the mixer deck, and switched the deck's input level to -10, to see if get 0 dbVU indicated on the deck? If I don't, I could try adjusting the Slate Tone level from the F4 to give me a 0 dbVU indication. That would give me something close to a calibration tone for future use, I think?????
 
Just a historical note.

On analog you would slate with tone bursts along with a voice slate. So take one a single burst #2 two bursts, etc. The reason was you could find things in fast forward (or reverse). You can't understand the vocal slate but you can easily count the "beeps". So the tone on recorders were not necessarily for calibration, though I think they were set up to be used that way, but they were literally "slate" tones. I don't know if they were ever really designed to be used like calibration tone generators you would use in a studio.

And of course they were not to set up equipment levels since they were the end of the line.
 
Your historical note seem to be exactly how it is implemented on the F4. A push of the button gives you that beep, and turning it on only seems to allow you to see if everything is connected correctly. Nothing else.
 
indiawilds said:
How are you tying or rigging the Zoom f4 to your camera setup?
Click to expand...

I integrate mine into my setup via a K-Tek Norbert Sport. It's been discontinued, but you might find a dealer who has one. I mount my F4 on it, and then have the camera on top of that. I then mount my rode videomic on the top of Norbert, as well as my wireless receiver.

If you can't find one, there are other versions of it out there that are similar, but more cheaply made that might work.

The F4 has a 1/4 x 20 hold on the bottom, and it comes with a mounting bracket that allows you to mount your camera to the top of it, so that's how you integrate it into a camera setup.
 
indiawilds said:
How are you tying or rigging the Zoom f4 to your camera setup?
Click to expand...

I use a 5 foot siamese cable when the mic's are on camera, the F4 hanging off my shoulder (haven't gotten around to buying a bag, yet). Off camera I use a 25 foot snake with a headset return included.

But, I ain't a pro, and you should take that into consideration.
 
graywolf said:
Your historical note seem to be exactly how it is implemented on the F4. A push of the button gives you that beep, and turning it on only seems to allow you to see if everything is connected correctly. Nothing else.
Click to expand...

Wich would be unfortunate since the tone is now used as a setup aid. I use the tone on the MixPre to set the recorder level all the time. I have tossed the tone on as a slate from time to time, usually when recording a sequence of SFX as slate tones.
 
True. I actually own a portable tone generator. I needed it for laying calibration tones back when I was recording to 1/4" tape so I'm covered.
Just seems to be a less than great choice to include a tone function if it doesn't work the way most people will want to use it.

At the end of the day once you know how it works I'm sure it can do the job. As long as you know where the tone needs to read on your camera meters you can still use it. I mean everyone is expecting to calibrate to -20 but really as long as you know what the number should be at the end to make everything happy you can just go with that.
 
Well, a zero db tone from the Shure analog mixer gives me -12db on the camcorders at a middle setting. A -12, or -20 tone from the F4 gives me a signal only a click from all the way up on the camcorders. The Shure calls it a calibration tone, the F4 calls it a slate tone. I do get a good signal from the F4 with the gain on the camcorders set to a mid level, however. So, to me, the problem is the Slate Tone.
 
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