With conventional 5.0 Surround recordings, made in acoustic spaces, there is a missing aspect in the reproduced Surround. We can get the acoustic space to horizontally ‘surround us’, but missing is the reproduction of the rest of the acoustic recording space, from above the mic rig’s position.

Adding four ceiling placed loudspeakers to a decent 5.0 Surround setup, can very effectively add this missing dimension, with appropriate microphone additions to a suitable basic 5.0 Surround rig. As covered in Paper No.3, ideally our playback set up of the five horizontal loudspeakers, should be as near as possible to the ITU intentions. From the ‘sweet spot’ best listening position, they should be in a full circle. The front L and R should be near 30 degrees either side of the Centre loudspeaker. The rear Ls and Rs are spaced apart much wider, at 110 to 120 degrees, to get an ‘acoustic dispersion’ around the listener.

The sensible approach to placing the additional four ceiling placed Height loudspeakers is to have, two either side of the sweet spot and another pair front to back, ideally all the same distance from the listener as with the usual horizontal 5.0 Surround setup. To a degree, this actually carries on with the traditional Periphonic approach from back in the Michael Gerzon days of research.

There has to be a proper relationship in the Height loudspeakers positioning to the microphone rig in use. This has proved to be conveniently possible with the additions to a number of the normal ‘horizontal’ Surround rigs, covered in Paper No.2.

A demonstration of the height facility to a 5.1 Surround playback the writer has just heard, uses two height speakers above the front L and R, and two more above the rear Ls and Rs. This actually rules out the use of all the ‘coincident’ mic rig approaches detailed later in this paper. Even more specifically, it seems to the writer that the use of the SoundField’s W, X, Y, Z way of providing height is ‘kyboshed’ by that way of adding the Height loudspeakers to a standard 5.1 layout.

For the record, the writer’s Monitoring and Mastering for Surround with Height, is a collection of active Klein & Hummel 300s together with three powered K&H 110s for the Centre plus the Ls and Rs loudspeakers. The four Height units are the smaller powered K&H 52s. Balanced feeds are provided to each of the nine loudspeakers involved.

THE MICROPHONES RELATIONSHIP TO THE PLAYBACK ARRANGEMENT

There is a point of view that, as the human head’s hearing system is quite ‘coincident’, compared to the size of the sources of the acoustics we capture, then it is best to have a ‘coincident’ set of microphones to start with. The spaced out loudspeaker playback reproduction, is then fed to the ‘coincident’ human head hearing system, as would be the case in the original acoustic space.

The writer has added the Height facility to a number of different microphone rigs, originally used for the conventional 5.0 Surround. The usual Stereo use is usually mixed on the day, with all the mic outputs separately laid down ‘raw’, on either an Edirol four channel, a Deva 5 or a Sound Devices 788 eight channel recorders, for the later essential Mastering for the full Surround.

SURROUND PLUS HEIGHT MIC RIGS USED

A bit of history first! Going back, thirty years or more, the Calrec SoundField microphone was at the heart of the concept of Surround, with the Ambisonic system of four loudspeakers used in a horizontal square. Even then, with its 360 degree spherical capture of the sound around it, Height was possible with Periphony, using two additional sets of four loudspeakers to reproduce the other two vectors in the true 360 degree world.

These additional sets of four speakers had to be in vertical ‘squares’ around the listening position – front to back and side to side. So it was not really practical, outside a University research environment, to have four of them around on the floor in a domestic situation.

The current SoundField microphone system carries with four ‘soft’ cardioids in a regular Tetrahedron, known as A Format. Early analogue matrix processing, and now done in the digital domain, produces the practical set of four B Format signals (W, X, Y & Z). The W is an Omni, with three Figure of Eights, X forward and back, Y side to side, and Z up and down. The latter is the provider of the Height facility.

Cardioids are produced, as needed by combining the figure of eights with the omni, and then Mid & Side (M&S) mixing takes the SoundField forward to all its uses. The ‘beyond’ now includes adding just the Height to 5.0 Surround, as being covered in this write-up.

The basis of stereo M&S mixing is that the Mid signal is fed in phase to both the left and right being created, with the obligatory, ‘Side facing’ figure of eight signal being fed out of phase to the left and right. Stereo width is decided by the level of the Side feed, compared to the Mid signal.

THE SOUNDFIELD MIC USE.

As mentioned earlier cardioid ‘mics’ are being created, with the W,X,Y & Z signals, by adding the appropriate figure of eight, in phase or phase inverted to the W omni. For Horizontal 5.0 Surround you would have one forward and one back, for M&S decoding, the forward one alone for the Centre channel. The Z figure of eight, in phase and added to the W omni, provides the upwards Cardioid. M&S decoding with the X figure of eight provides for the front to back Height, with the Y figure of eight providing the Side to Side Height feeds.

THE SENNHEISER COLLECTION

Three Sennheiser mics from my armoury have been incorporated into a rig useable across the board needed of facilities, from variable polar pattern mono, stereo, 5.0 Surround and now with the plus Height facility. A Sennheiser MKH800 Twin, with its two back to back cardioids, has a figure of eight Sennheiser MKH30 vertically coincident above it for the basic M&S, plus the Double M&S for normal Surround 5.0.(Pic. One)

The MKH80 above the MKH30 (Pic. Two) takes it into the Height regime, used switched to cardioid. The side to side height feeds are created using the MKH30 for M&S decoding. The MKH800 Twin is used as a figure of eight, front to back, for the other two height loudspeakers.

THE SCHOEPS CLUSTER

The use of four side address Schoeps CCM4v mics allows for the Double M&S decoding of the 5.0 feeds. They are facing front and back and side to side. The side to side pair are created into a figure of eight by inverting the phase of the right hand facing one and summing its feed with the left hand facing one. This created figure of eight is then used for the Double M&S 5.0 decoding.

In the middle of them, pointing upwards, is an end address CCM4 for the Height decoding, using figure of eights created from the appropriate pairing of two of the opposite CCM4v mics. Also shown is the optional use of Omni CCM2, at the rear of the cluster, which is used with a Schoeps ‘in line’ LP40U low pass filter, to assist the LF of the CCM4 cardioids. (Pic. Three)

THE DPA 5100 PLUS

The DPA 5100 is a light weight, very low handling noise and well wind proofed system for ‘out in the wild’ 5.0 (or 5.1) Surround capture. There is a way of adding an effective Height facility to this unit. It has been used for recording Thunder Storms, Fireworks, Aircraft Displays, Bird Song and even Steam Trains!

The interesting thing about making outside recordings in this way, is that the playback is not restricted to just the space between the use of a stereo pair of speakers. For instance a Steam Train can be heard as coming past from far left to far right, well outside the distance apart of the front L & R pair of loudspeakers, which is as far as you get in Stereo.

The DPA 5100 has five omni mics inside its inaccessible ‘bicycle saddle’ look (Pic. Four).  Hence the low handling and wind noise, compared to any usual directional mic, especially with figure of heights. However, the front L, C and R feeds in the DPA 5100 have actually a degree of directionality by having the three omnis, quite coincident in the middle of the unit, with short interference tubes, pointing appropriately to provide the directional effect.

The Ls and Rs omni are spaced out and flush mounted on the rear of the unit. There is a sixth LFE feed which is derived from the five omnis, but the LF still remains in all the five mics direct feeds. Ignoring the LFE feed allows for three additional omni mics to be added to the top of the unit for the addition of Height, enabling the use of an eight channel portable recorder.

Pic. Five shows the writer’s arrangement of the three flush mounted DPA 4060 omnis, using three of their ‘dismantled’ 48V phantom power accessories. Windshielding is initially with flour sieve meshes and ladies tights! (Pic. Six). On top of that, one can add an extra one of DPA’s windshield covers, having cut a hole in the one covering the original 5100, to allow access to the 3/8 inch bolt hole for fixing the extra mic’s plywood base.

So we have one height capsule front centre and the other two off to the sides, suiting the positioning of three of the Height loudspeakers playback. For the rear height feed the writer merely sums the Ls and Rs feeds for its use.

MONITORING & MASTERING ESSENTIALS

Apart from having the nine loudspeakers as near as possible to the layout discussed earlier on, it is necessary that their outputs be checked to be closely level matched and all to the same phase. If you have access to something like Neutrik Test Instruments (NTI) Minirator for Pink Noise, their Minilyser for level metering with their Mini SPL Test Mic, these judgement can be taken further.

With pink noise you will also be able to hear any timbre differences that each speaker deliver, and what effect their position in the room is causing! It isn’t too difficult to check that none are ‘out of phase’ by judicious head positioning whilst feeding pairs of the loudspeakers with the pink noise. The writer’s set up provides balanced feeds to each loudspeaker, with individual pots to set their levels when using the pink noise. It is also easy to provide each balanced feed with a phase invert switch.

Each of the mic rigs used need a different ‘decoding’ unit to provide all of the nine feeds needed, hopefully all properly phase related and not to far from having similar output levels. Before the final balanced feeds and output setting stage, mentioned in the preceding paragraph, there is the Mastering stage.

This Mastering stage has faders for all the feeds, plus a pair for a sub mix of any spot mics used to be mixed into the front L & R, for instance for soloists. It proved essential to have a phase inversion switch available for this sub mix, in case any phase miss matching is present.

Each of the pairing of channels, such as L & R, Ls & Rs, and the Height pairs are provided with variable width adjustments and there are trim level knob pots on all nine feeds. Apart from what you listen to on the accurately set up nine loudspeakers, there are a couple of totally essential visual monitoring systems available. These are the DK Technologies ‘Jelly Fish’ display with its 5.1 Level Bargraphs, or another product from RTW which has a ‘House’ display and the level bargraphs.

The writer’s set up makes use of the ‘Jelly Fish’, and two essential aspects to note is that a test tone on all five 5.0 channels produces a full circle, together with the Bargraphs showing equal levels (Pic. Seven). With all the different Surround recording done so far, the writer finds that when it sounds right at the sweet spot listening position, then the ‘Jelly Fish’ confirms this regularly by displaying near circular patterns with appropriate ‘wobbles’ coming and going.

Phase irregularities show with red sections in the display. Sometimes these seem temporally related to a venues acoustic, but anything seriously red indicates something is wrong in the decoding where the M&S process is involved. This seems confirmed when the DPA 5100 is involved, as it does not show up with its directly fed ‘unprocessed’ mic outputs.

How do you judge the Height feeds with the Jelly Fish? You arrange a switch which leaves the Centre channel feed connected to the instrument, and replaces the L, R, Ls and Rs with the Front to Back and the Side to Side Height feeds. Again, when these relate the same way on the Jelly Fish and the Bargraphs to the original Centre channel feed, what you hear is correctly being produced.

WORTH HAVING A GO AT IT?

The experiments carried out have indeed been well received by those who have sat at the sweet spot with a remote control that allows them to silently switch from Mono, to Stereo, to 5.0 Horizontal Surround and then to the Height addition. When they then switch straight back to Stereo, they all unanimously know that Stereo is ‘dead’ in comparison, as the reproduction of the ‘real world’s’ acoustic, collapses from around and above them!