Let's say you want to use mobile phones to record sound locally, but you want to be sure that they are all recording. One way could be to have an app that streams volume data to a server on the Internet. In that way you could have a web page that gives you an overview of all devices recording.

Audio-technica 4047

AKG P120

Samson C01U Pro USB

Take it for what it's worth!

So for the situations I tend to end up in, one-on-one interviews, conversations in front of a white board with 2 or more people and sometimes a group chiming in with opinions. here are some ideas with regards to wired, wireless, digital, number of inputs, where to record and so forth.

Insight number 1 — tracks

A video camera usually only has two sound tracks. If you want more mics than two, you will have to record those on a different recorder, being it a camera, a dedicated recorder or a sound card connected to a computer. This means that you need to do synchronization. Unless you are fancy with SMPTE or something, that will be done by matching audio automatically. If you already need to do that, it does not take much more time to match many tracks algorithmically.

Insight number 2 — synchronization

If you already accept synchronizing multiple sources, you might as well have the recording device on the subject. The exception being that two mics should be wireless and their receivers should be mounted on the main camera to get sound and images in lockstep.

Insight number 3 — lapels don't scale

It's a lot of work to mic people up. Well, not a lot of work but it does not scale to when you have 12 or 50 people. A handheld wireless mic which can be passed around can be a good option in those cases. Also, everyone understands how a normal handheld mic works, so don't go for one where you talk at the side of it or something. You could also use a portable recorder for this with built-in mics. Actually that may be the best option.

Insight number 4 — no digital

No need to go digital. It makes more and more sense in our day and age to go digital from the mic to the recorder, but since most cameras don't have digital sound inputs afaik, you'll have to wait for that for a while. And for your other devices, if one believes this blog post's insights to be true, you'll use portable recorders on the person, which come to think of it is kind of all digital, just a very short chain.

A possible setup from these insights

• Two wireless lavalier/lapel mics with the receivers mounted on-camera. You could go with just one and use the other channel for picking up ambient sound for synchronization
• Any other cameras used, can take up sound from any fixed mics, including boom mics, indeed they should use this to get some synchronization signal.
• Two people can be be mic'ed up with the wireless mics,
• any others can be mic'ed up with lavalier mics that go to a recorder directly on the person's body.

Being a bit more concrete

A. One wireless lavalier mic for the main camera,

for example Røde rødelink newscaster/filmmaker (untested by me).

B. More lavalier mics

All other lavalier mics used, would have their own recording device on the person's body. Here you would need to find good but affordable such recorders, or use mobile phones.

• Sony has an apparently great little mobile recorder under €100, the Sony ICD-UX560, but ideally you'd want to go a bit cheaper than that. Also, it does not come with a clip, but it does have a mic input with bias (3-5V for electret condenser mics).
• A mobile phone with e.g. the aputure a.lav mic. I have that one and I don't like it, though.
  

  I suspect some mobile phones apply compression, maybe there is a way to avoid that. Record that note App works well on Android as a recorder in my experience.

There are some novelties in the field, such as the

• Sennheiser Memory Mic, but I wish it came in black and not white. It's also at ~€200 a bit on the expensive side.
• Same price range for the Tascam DR-10L Digital Audio Recorder with Lavalier Mic .
• There is also the Zoom F1-LP, with lavalier mic, roughly the same price.

C. One handheld microphone

One handheld microphone that you can use for non-mic'ed up people to speak through. Here is a recorder that is of interest for this:

• Tascam DR-10X Plug-On Micro Linear PCM Recorder (XLR). Aroung €100.
• Here is one that even supplies 48V phantom power: Saramonic SR-VRM1 Plug-On Linear PCM Recorder for XLR Microphones, around €125.
• You could also use a handheld voice recorder such as the Sony ICD-UX560 (again) as a handheld microphone.
• Or even use a mobile phone, possibly with a mic sticking out to make it obvious where to talk. Make sure to have a good screen lock, but not so good that you can't unlock it because the finger print holder went to lunch.

Risks with this approach

• Uneven sound quality with so many different recording devices.
• Synchronization not working due to sound images being too different between different mics.
• It's hard to know with confidence if a local device is indeed recording. With a central mixing desk you could check. Maybe if you use phones you could have them report over the Internet their recording status.
• People wandering away with the devices.
  If a person wanders away with a wireless mic, you lose the mic. If he wanders away with a recorder however, you also lose the recording from that person! And you will have to edit them out of the video. A fitting punishment maybe :).

Go full insight— No wireless mics?

Actually for when only two subjects need to be recorded, two wireless camera mounted systems might be the best choice. Maybe one should never go go full insight, but you could probably get away with only portable recorders on the subjects, and sync up via the cameras' built-in mics. Actually for when only two subjects need to be recorded, two wireless camera mounted systems might be the best. But, you could probably get away with only portable recorders on the subjects, and sync up via the cameras' built-in mics.

With align-videos-by-sound, which is a python script/application you can align videos by their sound tracks.

After install, you can for example do this:

./bin/simple_stack_videos_by_sound_track --mode=direct --audio_mode=multi_streams tests/testfiles/3-secs-in.mp4 tests/testfiles/7-secs-in.mp4 tests/testfiles/full.mp4

It will present the 3 videos stacked in a "merged.mkv" file (one of the videos will be duplicated for symmetry), and the sound tracks from all 3 videos will be synced, for editing and mixing in e.g. Audacity (tested by me).

Click to view full-size image… — Size: 80.3 kB

This is what it looks like in Audacity when you open the "merged.mkv" file.

Align-videos-by-sound is alpha software!

sox stereo.wav narrowstereo.wav remix 1v0.6,2v0.4  2v0.6,1v0.4

Credit to here: https://superuser.com/questions/348756/creating-stereo-file-from-two-mono-files-with-sox

https://np.reddit.com/r/IWantToLearn/comments/apgslg/iwtl_how_to_create_a_better_environment_for/egaxmw5/

A proof to me that anything can be interesting once somebody explains it in a way that makes your brain grok the particular field.

This presumes you have been recording into the Canon C300 Mark I with two sound sources, split into separate channels. And you want the channels to be panned hard left and right, suitable for editing and comparison in e.g. Audacity (Although you can of course also export to different files and import).

This does the trick:

ffmpeg -i from_canon.MXF -filter_complex "[0:1] [0:2] amerge" -c:a pcm_s16le stereo.wav

Credit goes to FFMPEG: Need to mix dow multiple audio stream to single stereo - Stack Overflow

Software such as ffmpeg, Videolan Client (VLC) and audacity see Canon's MXF format as two separate sound channels inside a container, not as a left and right channel. In VLC you will only get one audio track for example, and you can switch to the other one if you want. So using ffmpeg, this won't work:

ffmpeg -i from_canon.MXF pcm_s16le stereo.wav

It will say that it will only include one audio stream in the wav file, althought there are two:

Stream mapping:
  Stream #0:1 -> #0:0 (pcm_s16le (native) -> pcm_s16le (native))

Mapping the channels into wav also won't work:

ffmpeg -i AA340601.MXF -map 0:1 -map 0:2 -c:a pcm_s16le all.wav

This will give the error:

WAVE files have exactly one stream
Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument
Error initializing output stream 0:1 --

I put the sound track down for a screen cast with my Sony bluetooth headset. The result was not good, I had to redo it later with a wired mic. I then saw a video review of a higher quality bluetooth headset, but alas again the sound is no good from the mic:

https://youtu.be/xbxyqSVc_Io?t=265

This answer on Quora seems to indicate that with current standards bluetooth microophone audio will always suck, unless you hack the mic stream into some data protocol of bluetooth.

Why is the quality of my microphone so bad when I use my Bluetooth headset with my windows desktop computer? - Quora

Not many sound cards I have found have multiple inputs for 3V electret condenser microphones. Maybe that makes sense, since such small mics are often used with headsets and as lapel/lavalier microphones, and those tend to be wireless if you're handling more than one.

Still, it would be fun to make a thingy that converts 48V phantom power to work with an elecret. Actually you can buy such an adapter off the shelf from Røde for about €20. That is probably the sane thing to do:

Rode VXLR+

However many people have thought about and designed their own solutions for this.

links

audio - Phantom Power supply for Electret mic - Electrical Engineering Stack Exchange

Convert 48V Phantom Power to 9V

This one is more about powering electrets in general, good read! Especially intrigued about just using two batteries in series and that's it:

Powering microphones

One of TI's examples is downregulating from 48V for the below circuit:

LM317HV 60V Input, 1.5A Adjustable Output Linear Regulator | TI.com

Towards a setup with a focus on redundancy and forgiveness — so that botching a recording will hopefully be a thing of the past.

What we ideally would like to have, is a wireless system with high mic capacity, where all mics are sent digitally into a sound card and presented as separate channels to the audio workstation of your choice, for processing and mixing. Also, it would be nice to have multiple systems recording in parallel.

We can't get all the way to that on a small or medium budget. But we can get somewhat close.

Last week I rescued a conversation/interview track from a good videographer where unfortunately different sound levels and noise levels had been mixed together into a mono mix. Since people took turns in talking it wasn't too hard this time to make it really good by applying noise reduction and normalization per-region.

And I guess we've all have experienced a recording, by us or by someone else, where one participant just isn't audible or where the sound quality varies to the point that the listener must wonder if the people talking are all in the same room, or even at the same event.

If you have an experienced team that interviews you, they know how to set up things and they will have a dedicated sound technician. I was interviewed by such a team (from German 3sat)  a few months ago. Flawless.

But if you don't have access to that and I don't most of the time, it can be interesting to explore what technology can do to help to make sure you do not botch the recording. Do note that the equipment listed below is untested by me, with a couple of exceptions.

B&H Photo Video Audio has an article that touches on some of these topics, although they specifically talk about field recordings: How to Use a Portable Audio Recorder in Field Production

Many microphones are better than few microphones

If you have many microphones, errors in individual setups will have less grave consequences

Wireless is king

Many interesting conversations take place that aren't solely for the benefit of the recording. We can't have cables all over the place!

Separate digital tracks into the computer

It's better to be able to process separate channels afterwards and compensate for different levels of noise, sound characteristics and the like. Also, you can get rid of tracks that were no good. This is often referred to as multi channel recording.

The audio should be converted to digital as soon as possible.

And preferrably not converted back and forth a couple of times.

Setups that try to meet these requirements

The solution that meets all requirements (almost)

I'm adding this here: Samson — Go Mic Mobile®

With the lapel/lavalier option, this is really cool since it is all digital. It's a wireless system with a receiver that can send two independent channels, from two wireless devices, directly to USB.

I'm tempted to "drop my mic" here. However read on for systems with higher channel counts and many more options.

Wireless microphone system

AKG DMS Tetrad ~€700

A 4 channel wireless microphone system that is digital, and has 4 separate outputs. Separate outputs is kind of rare under €1000. The digital wireless part should make it more robust against interference (all wireless mic systems are turning digital nowadays). The Tetrad also has separate outputs for each microphone! But alas, it has no digital out.

Microphone arrays

As a backup, an advance conference microphone system may be good. This one has 4 microphone arrays and automatically listens in the direction of the current speaker. It has good reviews but not sure if everything is also available over USB and not just Bluetooth.

Bluetooth Speakerphone - eMeet M2 Black Wireless Conference Speakerphone ~€200

A cheaper version with no arrays is this (tested by me, ok) and it works well over USB:

Jabra Speak 510 UC USB/Bluetooth ~€100

Multi-channel sound cards

Some sound cards only allow stereo digital output, others offer 4,8 or 96 outputs for that matter. Sometimes it depends on the drivers and operating system in the computer how many channels you get. Behringer UMC1820 and Behringer UMC404HD  work well with Linux according to what I could read at LinuxMusicians— Linux support Behringer UMC404HD?.

My guess is that all cards below work well on Linux. OSX also does a good job with multi-channel while Windows struggles and needs bespoke drivers.

What is a channel

With "channel" below is meant the whole chain: An XLR/phone input with a mic preamp on the card that turns up as a separate channel in the computer's audio workstation.

Compact studio cards

Behringer UMC404HD  Four 24-bit channels. ~€100

Cheap, compact.

Focusrite Scarlett 18i8 2nd Gen ~€300 An eight channel 24-bit that is not a 19 incher for rack mount, but much more compact

19" studio cards

Behringer UMC1820~ €180 Eight 24-bit channels + ten virtual Adac ones.
Cheap, 19" for rack mount.

Behringer ADA8200 Ultragain ~€150 Eight 24-bit channels.
Cheap, 19" for rack mount.

Portable with extra built-in mics and built-in recording

These recorders function just as the above sound cards, but add the ability to store multi channel recordings directly and in parallel on the device, and are eminently portable and have a couple of replaceable microphones built-in.

Zoom H5 Handy Recorder | Zoom ~€250 Two 24-bit channels + 2 more with a separate clip-on adapter for ~€60

Zoom H6 Handy Recorder | Zoom ~€300 Four 24-bit channels + 2 more with a separate clip-on adapter for ~€60

Built-in recording and audio work stations

These work stations can function just as the above sound cards, but add the ability to store multi channel recordings directly and in parallel on the device, and are also mixing desks with a lof of hardware knobs and faders. It's really cool, but more to lug around and may look a bit intimidating to the participants.

Zoom LiveTrak L-12 Fourteeen 24-bit channels ~€500
Here is an inspiring video. Zoom LiveTrak L‑12 | Mixing pop/rock song - YouTube The multi channel source files are from a reference library, free for people to try their mixing chops on. Gorgeous song and singing voice, if you ask me! Some people report bleeding between higher track numbers for this device. Some of the channels on this one are not pre-amped.

Zoom R16 Eight 24-bit channels. ~€330
An oldie that still seems to give the best bang for the buck. Some of the channels on this one are not pre-amped.

Shoestring option

Some Linux distributions such as Ubuntu Studio with Ardour and Jack should be able to record from several sound cards at once. In fact I will try this a bit later with some old sound cards.

Here is a wireless microphone that records straight to USB: Fifine.

Not sure it's digital in the wireless part though.

Synchronization with video

One option is to record through the video mic and then use software that synchronizes your multi channel stuff with the video. One piece of software that does this is the python script align videos by sound. I maintain that software, but other people are the ones that have coded it, I just smacked a command line interface on it. I have used align videos by sound to synchronize a mobile phone voice recording with the video camera's internal mic recording, and it worked fine, reporting the correct offset.

General sound into the video cameras

In order to sync with video. the cameras should record sound even if we will not be using that sound, since it will be used for syncing. Conversely, one of the mics going into the multi channel card should be close to the camera mics to pick up the same pattern.

Redundancy

One option here is to mic up each person with two mics, and simply let the second mic record to the person's phone (or other phone). I have an Aputur A.lav lapel mic that can do that, but not happy with it. Worst case, just use the internal microphone of the phone!