I just finished going through the stack of emails that needed my attention and responded to a bunch of comments on some recent posts. The 16-bits vs. 24-bits debate continues to draw comments. I’m planning on going through the John Siau article in detail with illustrations and possibly even some animations to reinforce the concepts that he so skillfully wrote about. It’s proven to be a difficult subject to explain and for many to grasp…stay tuned.
I got a curious email the other day regarding the idea that my recordings are not worthy of evaluation over at the AVS Forum’s CD vs. HD challenge that Scott Wilkinson and I concocted. In spite of our insistence that the test is neither scientific or the results indicative of anything, it’s received a lot of attention, over 2600 comments, and stark positions on both sides of the issue. We’re planning a “Home Theater Geek” podcast to go over the challenge and talk about other current high-resolution topics in early September. He had asked whether some of his audio writer associates would care to take the challenge. One of them sent along a question that seems somewhat curious.
The author wrote, “I’ve got most of the AIX Records and I’ve met Mark and discussed his micing technique. He uses multiple stereo pairs. He then ‘time aligns’ the waveform so the impulses line up, which is what most multi-mic recording engineers do during the editing process. But aligning the impulse attacks does not phase align the sound.”
Because of this, he declined Scott’s request to get involved. His reasoning was that my tracks were too “phase compromised” to be of any use in an A | B comparison.
Phase “compromised” is a description that I’ve never heard before. It sounds a little like a disease that audio recordings can fall prey to if the recording engineer is not careful. Honestly, I can only imagine what the author was thinking. But I can assure him and the rest of my customers and readers that I do not “time align” the waveforms or audio tracks associated with any of the tracks that I capture…stereo pairs or not. And while I am familiar with the process of aligning tracks in commercial recordings, it’s not a procedure that “most multi-mic recording engineers do.”
Imagine the following scenario. You’ve been hired to record a concerto (a concerto features a soloist or soloists in combination with a full symphony orchestra i.e. Beethoven’s Violin Concerto). Traditional miking technique would have you place a stereo pair (Blumlein or ORTF or spaced omnis) above the orchestra about 15 feet behind the conductor. You might also place a dedicated mic or stereo pair near the soloist. Because the two pairs of mics are some distance apart, the signals from the close mics and more distant pair will not be “time coherent”. It takes more time for the sound to reach the farther pair of mics.
Figure 1 – The is the track layout of a Pro Tools session showing the “delay” of a stereo pair due to distance. Some engineers would manually move the tracks…I leave them alone. [Click to enlarge]
When summed electrically during a mixdown session, the difference in time will cause a very slight phase shift and “muddy” the sound. So in somewhat rare occasions, audio engineers will manually align the signals coming from the different locations. I don’t.
I use a large number of stereo pairs and mono microphones placed quite close to the source instruments or voices. They are all about the same distance from the source sounds and therefore are “time coherent” with regards to each other and don’t require or need any “time aligning”. The omnidirectional microphones at the back of the hall are the only ones that might have some timing issues but they are used for reverberation and don’t compromise the phase of the main source tracks.
Even if I did manually adjust the alignment of my stereo signals, it still wouldn’t nullify using my recordings for a comparison between CD resolution and HD-Audio specs. I don’t understand why the author of the question just didn’t politely decline Scott’s invitation to participate rather than fabricate a flimsy excuse…one that isn’t true.