The C-trilogy (Part 1) - Center, who are you?

According to Wikipedia "It is the channel that is mostly, or fully, dedicated to the reproduction of the dialogue of an audiovisual program. [...] In material without accompanying visuals (eg music), the center channel simply reproduces sound intended to come from immediately in front of the listener."

The center channel serves to anchor the phantom image which widens the sweet spot for listeners. On the other hand leaving a discrete--and required--signal out of the L+R channels will cause a problem if the C channel is not configured correctly. Insofar many engineers also feed this material to L+R. See the discussion @ mixonline.

In the C-trilogy I'll do some thinking aloud about (1) which microphone to use, (2) where to place it and (3) how to add it to the mix.

Which microphone to use to supply a discrete signal for a dedicated center channel?

Sidetrack: I say "discrete signal" because with coincident main microphone setups (XY & Blumlein; M/S provides you with a dedicated C anyway) you can easily extract the sum of L+R and place that onto the C. This works slightly less good with near coincident arrangements (ORTF) and not at all with time of arrival based / AB setups.

What you want to do is find a spot where you'd place the one microphone required for a monophonic recording. True, this skill has been steadily devalued, but attempting it lets you appreciate stereo and surround all the more--and gives you something fitting the C.

• Cardioid: A microphone of cardioid characteristic attenuates sources arriving off angle. Using one will work only if the ensemble does not expand far in width and depth. On the other hand you will attenuate sound sources from behind the microphone, e.g. favorably reducing audience noise.
  
• Omni: I generally consider an omni, with a uniform frequency response in all directions, to be a good choice to track a dedicated center, especially if it can be placed close to or centrally within the ensemble.
  
• Bidirectional: A fig-8 can also be used facing sideways in a close frontal location, but not centrally within a heterogenous soundfield, e.g. an instrumental ensemble. It works well for a choir, attenuating vocalists singing towards the mic as well as sound / noise coming from the direction of the audience (and conductor).

When recording repertoire with one soloist a close spot can also be fed to the C, suitably delayed (in relation to the main microphone) if you don't want to pull the soloist to the middle--which can be an option on occasion. You'll probably want use a directional mic in this case to have greater control over the pickup range, but if you are close enough an omni will work as well.

[Continued in Part 2]

Recording in Surround, _not_ in "5.1"

• Do you have to use a spaced-pair technique (AB or runtime-stereophony) when your speakers are placed apart?
  
• Are you forbidden to toe in your speakers when the microphones that were used to make the recording were placed in parallel?
  
• Do you have to stand one loudspeaker atop the other to play back a coincidence-stereophonic take (XY)?
  

The answer to every one of these questions is: No.

The configuration of the listening environment does have an influence on the requirements of the recordist.

• The number of channels recorded or mixed up to / down to is--though not linearly--dependent on the number of speakers in use.
  
• The balance of front and rear has an influence on the nature of information the recordist will want to capture.
  
• If raised speakers are to be used in playback that has to be taken into account when tracking the session; currently a rather unusual requirement.
  

Still, when planning for a recording (primarily) intended e.g. for reproduction on a 5.x system your main microphone configuration does not have to mirror the constellation that will be employed for playback.

What you'll want to capture is a frontal soundstage, with adequate detail, combined with as much "room resonance" as required. For 5.x the latter will amount to a minimum of two microphones recording clean, uncorrelated ambience that can be positioned at the back left and right for spatial envelopment. For the (more common) horizontally level interpretation of 7.x you might decide to use four "ambient spots"--unless you intend to extend the soundstage to full left and right.

True one-point stereophonic systems, with the exception of the Blumlein-setup, employed preferably in great sounding spaces, in my opinion rarely can create a pleasant stereophonic image on their own. I feel the sound design often benefits by some "sweetening" through runtime / phase differences. One-point surround microphones exhibit the same problems--in my listening experience. But that is a separate topic.

Recording on the run

What do you need to record the best possible sound (in stereo) while spending a minimum?

You need...

• High resolution microphones
  
• A pair of professional grade microphone preamplifier
  
• A transparent Analog Digital Converter (ADC)
  
• A digital recording device

With regards to microphones, small omnidirectional capsules are quite immune to wind noise and have a flat frequency response over the relevant spectrum. I am a big fan of DPA's miniature 4060 capsules. They have a healthy output, are reasonably quiet and don't color the sound.

As a 2-channel high quality micpre & ADC I am partial to Metric Halo's ULN-2. It can be battery (or FW-bus) powered and offers astounding sound quality. The 2d-expanded version is even more powerful than the original, but the former is less expensive while offering all a field recordist could wish for.

As for the final component, a digital recorder, you can either use a portable Apple Macintosh, connected to the ULN-2 via FireWire, or a Compact Flash recorder--with digital input! I hesitate to recommend M-Audio's MicroTrack II, but for the price nothing compares currently.

The above setup will cost you approximately...

• 0900,- US$ (2 x DPA 4060 + XLR-Adapters)
  
• 1200,- US$ ULN-2 (The current 2d-version retails for about 1700,- US$)
  
• 0250,- US$ (MicroTrack II)
  
• ------
  
• 2350,- US$

And before you go shouting please remember my initial premise: I aim for "the best possible sound" with no compromises. I didn't say it would be cheap, but this investment is well worth it :-)

For comparison purposes, here is a selection of professional integrated solutions (micpre, ADC, recorder) used in the film business, some of which are way outside of moderate budgets:

• Aaton Cantar-X2
  (5 x mic + 4 x line + 8 x AES/EBU)
  
• Nagra LB
  
• Sonosax MiniR82
  (2 x mic or line or AES/EBU + 2 x line or AES/EBU + 4 x AES/EBU )
  
• Sound Devices 702
  
• Zaxcom ZFR100 (+STA100 for stereo)
  (This one is actually quite inexpensive)

Sidenotes:

• The 4060's are nearly invisible and easily and unobtrusively placed where ever you like, even over your earlobes for head-based recordings--not that I endorse that approach.
  
• The 4060's will give you years of pleasurable recording, with all kinds of repertoire. OK, you'll be restricted to AB-stereophony, but you can always get other microphones later. Like 2 cardioids for ORTF, e.g. a matched pair of Rode NT5.
  
• You'll be able to use the ULN-2 as an amazing sounding preamp for analog & digital sources, driving your power amp directly, with monitor level control in the analog domain.
  
• The MicroTrack (usually) does what it's supposed to, but I've had several complaints about the original model that I am not certain have been resolved in the meantime. This calls for a separate blog-entry.

...

See also: The Digital Audio Field Recording Equipment Guide by Andy Kolovos.

Metric Halo (MH Labs) audio interfaces for high end consumer audio

Why should sonophile music lovers not use the best equipment the professionals use as well? OK, some of them might not have need for microphone & line inputs as well as a multichannel ADC, but the rest of the package should appeal to you in any case.

• 2ch (ULN-2) or 8ch (2882 and ULN-8) output
  
• digital inputs (S/PDIF and AES/EBU) with an amazingly transparent DAC
  
• A great preamp to directly feed your power amp
  
• A great headphone output
  
• Pristine complex DSP-matrix processing, e.g. for modeling digital crossovers, speaker-tuning etc.
  
• "Character"-options
  
• FW-connectivity (Mac only)
  
• In the case of the ULN-8, digital control of all analog output levels,
  
• with a frequency- & phase response flat from DC to Nyquist.
  

Check them out!

The ULN-2 is the 2-channel incantation with hardware knobs, analog volume control and 10 user-definable presets.

The 2882 is the 8-channel incantation that offers complete digital control via a connected Mac. Great for multichannel (5.1, 7.1) setups.

The ULN-8 is the top of the line technically and audio wise. But if you don't audition it you won't mind missing out on the fun ;-)

One final note about 2d: This add-on card improves the accuracy of the built-in clock and of the PLL (for extracting clock from external sources) significantly, and frees up the internal DSP by handling the channelstrip-based mixer, but you probably could do without as a non-pro, so go for it if you want to save some money and can find a used interface that has not yet been upgraded. I have enjoyed their sound for years and believe you will to.