Скачать или смотреть [MIC TECH ANALYSIS 5]: DECCA vs BPT (3 capsule microphone systems)

What you are seeing is NOT A FREQUENCY SPECTRUM ANALYSIS, but the Frequency-dependent Cross-correlation Coefficient “FCC” for the two channels of a stereo recording, as measured by MAAT’s “2BC multiCORR” VST-PlugIn. The visual result is – of course - based on the combination of direct sound + diffuse sound arriving at the membranes of the two 3-capsule techniques DECCA and BPT.
The FCC is like a 'fingerprint', which is characteristic for each microphone technique.

The figure citations in the text below refer to this book:
Edwin Pfanzagl-Cardone „THE ART AND SCIENCE OF SURROUND AND STEREO RECORDINGS“ (SPRINGER Nature); https://www.springer.com/de/book/9783...

1) With the DECCA technique the listener immediately gets a quite convincing localisation of the orchestra in the recording venue. One thing a critical listener could object to, is the exaggerated 'stage depth' as the string sections sound quite close, while the woodwinds sound (too) far away and are - in comparison - too low in level, at least in the 'tutti parts'. Hence, the need for spot mics for woodwind, brass, etc arises.
As can be expected with an AB recording (even though involving 3 capsules this time), below a certain frequency signal correlation tends towards mono, and usually stays well above a value of 0.5. (see Fig. 8.2)
2) The FCC measurement of the BPT (Blumlein-Pfanzagl-Triple) technique has a very different characteristic: with the STRING QUARTET recording FCC is usually very low and at times largely negative (with values occasionally even touching on -0.8) for frequencies below 200Hz. This is not a bad sign, as we know from research that low signal-correlation at frequencies below 500Hz (and even more so below 200Hz) are vital for good spatial impression. (for more literature references on “spatial impression” see    • NEVATON-BPT Concert for Piano and Orc...   )
At frequencies above 1kHz FCC is usually around 0.3 for the BPT.
Considering that the NEVATON BPT-mic had been suspended with the recording of the following octet-performance (from 4:19) in mind (and is therefore not in an ideal position for capturing the string quartet) the recording nevertheless sounds very nice and shows one of the unique strengths of this technique: due to the enhanced directivity of the fig-8 patterns in combination with an absorptive panel behind, this system is very ‘far reaching’ an can easily be placed outside of the ‘reverb radius’, without losing definition of the sound source. As can be seen in one of the graphics (section: “BPT-mic far-field positioning” at 7:11), this results in achieving a kind of ‘new’ mic pattern, the “half figure-of-eight”. The BPT is also very special in the respect that one can use the fig-8 level attenuation (5:40) which ‘kicks in’ quite fast for sound-sources going off-center as a creative tool for level balancing (see graphic @ 5:44). This feature can be used to rebalance close-up instruments in relation to those further away. Thus even rather exotic BPT-Mic positions behind the feet of a conductor (see 5:55 at Teatro “La Fenice” in Venice) – if need be - , or in front of the feet of a vocal soloist (6:15), accompanied by a mid-size ensemble can make ‘sonic sense’ in terms of level balance, as well as direct-/diffuse-sound ratio.
Despite the fact that the BPT-technique – if balanced correctly – can achieve a high degree of “spatial impression”, I nevertheless suggest to use it in combination with “large AB” omni ‘outriggers’ whenever possible, as these – of course –manage to introduce an even stronger feeling of spaciousness, due to the additional ICTDs (Inter-Channel Time Differences) involved (6:02).(see chapters 1, 3, 4 for more details).
With the measurement of the OCTET-recording (from 4:19) it is interesting to note that the BPT-system at times displays a stunningly even distribution of FCC, when single notes of some instruments are played: this shows clearly that this technique is able to convey the actual phase relationship of the sound-waves (as impinging on the 3 membranes) in a very ‘clean’ fashion, without ‘superimposing’ a ‘phase-offset’ or particular, frequency dependent phase (i.e. cross-correlation) relationship due to the microphone technique itself, as is the case with AB recordings, for example (see Fig. 2.4 and 2.5). In that sense the “Blumlein-Pair” of crossed figure-of-eight microphones (which is the basis of the BPT) holds a truly unique position in that it delivers completely 'neutral', de-correlated L and R channel signals (in respect to diffuse sound), and even for direct sound it can be considered ‘ideally de-correlated’ in respect to its signal pick-up characteristics. This is also one of the reasons why the Blumlein-Pair is considered to be “very naturally sounding” [see Streicher R, Dooley W (1985) Basic Microphone Perspectives – A Review. J Audio Eng Soc 33(7/8)].

NEVATON BPT-mic orchestral recording:    • NEVATON-BPT YSP2019 ("NATURAL PERSPEC...  

MIC TECH ANALYSIS Part 1:    • [MIC TECH ANALYSIS 1] Stereo Main Mic...