LP Post-Production Rework for Release Project
A personal production project which has been recently initiated consists of back catalogue material originally intended as two separate releases - an EP and an LP - being reworked into one conceptually continuous LP delivered for surround sound playback intended for event showcasing.
Initially these two sets consisted of the unfinished LP, and the ambiguously releasable EP :
- [Set 1] The Ocean of Motion - 14 Instrumental / Electronic tracks orientated around an oceanic aesthetic, arranged with midi programmed software instrumentation and instrumental layering from guitar / keyboards.
- [Set 2] Mercury’s Ellipse - 8 tracks including 5 remixes - aesthetically oriented around dimly lit backroom spaces of a large tanker ship with it’s textural transitions between tracks cultivating a soundscape setting to reflect this.
However, following the production of the latter - it became apparent that some of these tracks would potentially not be releasable for a considerable amount of time : notably a remix of one artist’s, which after indirect consultation with their management it was made known that this couldn’t be released for 12+ months. With the unfinished LP being back catalogue for quite some time, with no clear route to it’s finalisation for release - overtime it became under consideration that these two sets could potentially be merged to create a tracklist with these continuous themes throughout - having these relevantly related oceanic aesthetics.
When I was approached by a colleague with the proposition to showcase a tracklist for his upcoming event, I took the opportunity to reinvigorate these projects with the aim to combine them in this way for this showcase. For further background, the EP was produced utilising a bespoke method of surround sound audio rendering - utilising spherical ambisonic sound fields to encode virtually acoustic qualities - hence the surround sound format showcase. However, due to the technical specification of this bespoke rendering method consisting of 2-channel stereo audio despite it’s surround sound properties, for this showcase event a full 7.1.4 configuration of Dolby Atmos will be in use. Therefore, along with the post-production tasks of compositional track rearrangement, additional overdub recording, return to the mixing stages, and cutting-floor type decisions going over the extended track count arrangement - there is also the delivery requirement to format and master the final reworked set for 7.1.4 playback.
Going into this from a post-production stage in this iteration of these two previously produced works, with the aim of combining them being on the basis of artistic consideration - practical work within this project largely consists of these later stages of overdubbing / refinement / tracklist arrangement, with consideration to the qualities of the works produced across creative conceptualisation and practical contingencies.
Post-production begun with the combination of track listings, with the conceptualisation seen throughout the final arrangement. Trialling the track playback before the event showcase has been key to ensuring that the conversion to surround sound formatting has been done correctly. As the audio system in use for the production is utilising binaural stereo mixdowns for monitoring surround sound - taking the project into a dolby atmos suite to properly check conversion on physical surround sound hardware has been required to fully emulate the event format environment.
Two iterations of full audio conversion and monitoring have taken place in the post-production stages -
- Following initial ideation, playback testing with stereo audio tracks assigned to each atmos speaker was tested - the result was phasing and did not maintain the intended soundfield.
As this bespoke VA audio is a stereo representation of a soundfield [360 Sphere Image], it can be stated that e.g. the left channel projects the left side hemisphere / the right channel projects the right side hemisphere - to create the full ambisonic soundfield sphere around the listener. However, whereas with conventional stereo this is intrinsic to the audio file due to its rendering process - it is required that the audio be rerendered so that each individual speaker of the 7.1.4 sound system projects its correct corresponding portion of the sphere.
With that in mind regarding the initial iteration playback test, it is clear that phasing issues would occur - as each of the 12 speakers individually projected a hemisphere, resulting in six images of the one sphere. What is required is for the stereo soundfield image to be re-rendered into 7.1.4, so that each of the individual speakers correctly projects its corresponding portion of the one full image.
Going forward then, it was established that re-renders in the correct surround format would certainly be a required export stage of the post-production process. This was undertaken in the second iteration, where the tracks were exported to this specification - to be taken and tested on the atmos system.
- Second iteration test was with audio rendered spherically to 7.1.4, however due to limitations within the DAW used for generation of the master project file (being Incompatible with 7.1.4) - a re-render in 7.1.2 has been required. As the surround format file output did contain all channels needed for manual assignment from 7.1.4 to 7.1.4 in the atmos system, this was tested. However, it became apparent that the assignment to the top speakers would not be correct. It was also noted that the LFE level required lowering.
Regarding now only the 4 top speakers, it became apparent that the assignment would not be correct due to the soundfield aspect of the audio format. With limitations in only being able to assign one audio channel to both corresponding sides rather than the required 4 to create the full image of constituted of 4 quarter segments [e.g. 1Ch routes to both Ltf / Ltr, rather than 1Ch routing to Ltf & 1Ch routing to Ltr]. It has been identified that another approach to rendering these top speaker signals is required.
Included is an illustration of the issue arising from the limitation of this channel to speaker assignment. The left image illustrates a cross-section of the intended top sphere image, whereas the right represents the incorrectly assigned playback where the rear image is incorrectly identical to the front.
In audio delivery processes, it is crucial to ensure technical specifications are thoroughly considered and implemented to ensure playback is as intended. Although in this scenario the requirements are both obscure in their technical definitions, and nuanced in their application - given that it is not standard practice to work 2-Ch stereo signal encoded with ambisonic multichannels, into a playback format such as 7.1.4. - however it does emphasise the importance of having a clear understanding of the technical requirements at hand. If this was undertaken with no prior knowledge of the material, inconsistencies in its playback would have unintended consequences which could negatively impact the immersion at the event. Given that the event is highlighting the use of immersive audio technologies, these requirements are crucial for a correct presentation of this audio rendering technology.
Included is a diagram illustrating the original rendering process for the stereo soundfield audio files utilised for this re-render process from 2-Ch stereo to 7.1.4. The stereo recording at the output of this rendering process is the initial material at hand.
This signal [intrinsic to the LP tracks], is then in effect spherically re-rendered via conversion into 7.1.4. As seen in this screenshot below - where the stereo signal from the diagram above essentially routes [via arrangement] to Bus 1 of the aux channel named “Surround”. This aux then uses surround panning, to properly utilise the multichannel configuration and to correctly rerender each corresponding signal portion to the correct individual speaker in the array.
In the transferring process from the project’s original stereo format, direct conversion to 7.1.4 was not possible due to software limitations. However, utilising a 7.1.2 conversion - the two channels of overhead speaker signal could then be assigned individually to both pairs of front and rear overheads. Utilising the figure above on overheads incompatibility, what this means is that each LR side speaker outputs its correct half of the stereo image as expected. Whilst this does double up the height section of the stereo image, during the third iteration playback test it was apparent that these assignments would be the best case-scenario as phasing was not present, with the height information only emphasised.
One area which was particularly convoluted was the manual assignment process between channel output and speaker signal. Due to the inconsistencies across software (Logic Pro X / Pro Tools / Dolby Atmos) in the way that it handles the process / metre order of surround sound channels - reordering was required to correctly assign speaker signal. Whilst signal is metered in the clockwise order for Logic Pro X (as displayed above), it is outputted in an unstated combination of SMPTE and Film surround channel order - with Dolby Atmos then expecting the Film channel order as input. Rectifying this was essential for proper signal assignment.
