Recording natural Instruments for 3D and Object based Purpose
In this article, we discuss the complex aspects of object based recordings with real instruments in a “realtime surroundment”. We will show, how typical problems of object based recordings can be solved, be it for headphones or speaker based playback.
- What is the meaning of object based recording?
- Recording purposes
- Playback situations
- Challenge in object based recording
1 – What is the Meaning of Object based Recording?
Basically, object based means, that single sounds, which are called objects, are no more placed in a room related system. Instead, all objects are recorded separately and will be placed in a virtual room based on meta data.
This system allows to adapt to the used playback system and room by scaling the objects. This is very important for movies and cinemas, as cinemas can have very different sizes, amount and placement of speakers. Dolby is using object based recording for their Dolby Atmos system. Dolby Atmos studios and Cinemas need a special Dolby certification, that mainly determines the position of the speakers based on certain parameters.
It also allows to adapt to headphone playback, as virtual 3D playback on headphones.
The opposite system is the so called “channel based system”, which is based on common recording techniques. All positioning and room related signals are fixed, and will be processed during the mixing.
Fraunhofers MPG-H system is a mainly algorithm based system that will encode multichannel audio signals into a stream. The good thing with the Frauhofer system is that it is independent of channel or object based. It can serve both systems and is used by several countries and organizations, like China and South Korea, but also by Sennheiser, Sony (Sony 360 degrees) or Samsung
2 – Recording Purposes
There are many kinds of recording purposes and situations, where object based recording makes sense or better said; has a very high relevance to be used:
- Classical recordings for headphone 3D
- Educational apps
- Live orchestra with amplification and other players like a rock band
As described before, the basic idea behind “object based” is, that you can cover many playback situations with the same basic recording. This may not work in all situations, however, in the case of a loudspeaker playback, systems like Dolby Atmos are able to scale the audio information according to the size of the room, and the amount of the speakers.
In all headphone-based playback situations, there is a big advantage in object based recording, in a way that single objects can be moved around in the “3D headphone field”.
Of course, there are always the discussions about localization in a headphone playback. However, this is not the topic in this article. Experiences in this aspect are very wide and partially have a long history, as it goes back to the times of dummy head recordings.
Educational apps can be very interesting and might lead you through an orchestra or a museum as an example.
Finally, when it comes to recording an orchestra in a way, where you are facing many “external disturbing” aspects, it can be very important, to pick up the instruments of the orchestra very directly, but still keeping an optimal sound quality which matches the need of classical, natural instruments plus the symphonic sound of a whole orchestra.
All these recording situations are based on the condition that the single sounds and instruments etc. are acoustically isolated from any other sound source.
As this is usually possible with many kinds of sound effects or studio recordings, like with rock bands, this is not possible when recording natural instruments, as long as you like to keep them in their “natural environment”.
3 – Playback Situations
According to what was discussed already, there are several playback situations:
- Any kind of stereo, surround and 3D.
- Multi speaker systems for 3D up to 22 and more speakers.
- The use of special systems such as Ambisonic.
- Soundbars, which can produce a 3D sound just with one unit, placed in the front of the listener.
- All kinds of headphone playback.
4 – Challenge in object based recording
Recording natural instruments for the purpose of object based recording and post processing is a huge problem, or let´s say a challenge. There are three important aspects, that usually interfere with each other.
- Sound-quality, mainly meaning natural, original sound.
- Optimal crosstalk suppression.
- Recording all instruments together in their natural playing situation.
These contradictions usually lead to unsatisfying results. Using a classical mic setup with common high quality spot mics will not result in cross talk suppression as it is needed.
Using common contact microphones will lead to unsatisfying sound.
Separating instruments and recording them one by one, as an example in anechoic chambers not only leads to very bad sound, but also to musical problems, such as extreme intonation and rhythmical effects.
The article will show a completely new approach to recording instruments for object based recording. The REMIC MICROPHONES instrument specific microphone system allows for recordings with a perfect crosstalk rejection as well as an optimal natural sound. Also, the REMIC instrument microphones can be attached to the instruments in an easy way.
These new recording options will lead to perfect results in all kind of situations as 3D recording, Games, VR, AR and any kind of situation, where instruments are needed in a separated way.
The important aspect is, how to find a perfect compromise between a good sound and optimal crosstalk rejection. This may not be necessary for normal „classical-classical“ recordings.
Every recording, which is not a „standard classical-classical recording“ will very likely need a special treatment.
Why is it a problem to record instruments in „inappropriate rooms“? – and what is an in „inappropriate room“?
Instruments, especially classical intruments, like strings or woodwinds, need a good room with natural reflections and reverb in order to produce their sound in the way it is supposed to be. (You may find other opinions about this aspect).
If you put a string in a very small and „acoustically dead“ room, the sound of the string will be dead as well. Here is why; Not only is the instrument „playing“ the room. The room is „playing“ the instrument as well! The reflections of a room have an important influence on the sound beaviour of the instrument itself, meaning that the reflections of the room will directly make the instrument vibrate based on the reflections that are coming back from the walls.
A simple example: If you play any drum of a drumset, all other drums, cymbals and further instruments, like a grand piano in the same rooom will start to vibrate as well. This is caused by the direct sound of the drum, but also by the reflections in the room as well.
This finally means that it is not possible to bring an instrument „back to live“ if it once was recorded in a liveless acoustical situation.
Some people might still remember the times of those horrible dead drum cabins, that were partially used in the 70s and 80s. The snare sounded usually horrible dead and dull, and you would need a lot of EQ‘ing to bring back the bright sound that you would like to have.
On the other hand, if you look to wonderful studios as the Abbey Road Studios in London, where The Beatles and Pink Floyd recorded, they are having great and big rooms, which were used by those bands to achieve their sound.
Delay Situation in common Orchestra Setups
Above: Illustration by Gregor Zielinsky.
This picture reflects the delay effect, which is happening in an orchestra recording based on a simple example with two instruments.
On the left side you find a “loud” instrument, represented by the circle. That could be any kind of percussion instrument, but also a trumpet or a piano inside the orchestra. This instrument is having a spot microphone placed pretty close to the instrument.
On the right side, you find a simple 3D main microphone setup. The typical delay between the spot and the main microphone in a mid sized orchestra will be around 40 ms, which is equivalent to around 11 meters. (Please be aware that these figures only serve as examples).
Many engineers will compensate for this delay. Spot delay compensation is pretty easy today using simple delay plug-ins, which cost no relevant system resources. In the case of a drum, this is a real life safer, as a delay of 40 ms will cause a detectable “flam” on the drum sound, meaning it will be heard twice, like with a short echo, which would lead to completely unusable results.
In addition, we find a second sound source, which is reflected by the small triangle in the middle of the picture. This could be a violin for example, which has a typical delay of 10 ms between spot and main mic, depending on the position of the microphones.
Of course we do not only have one main microphone to relate to. Actually this is making the situation more complicate. For our explanation here, we will not take this in our consideration.
We need to be aware, that the drum will clearly be heard on the violin microphone. This might be a delay of 20 ms.
As it can easily be calculated, we are running into an offset of 10 ms, which is the difference of the delay of the drum minus the sum of the spot delay of the violin microphone plus the time the sound of the drums need to reach the violin mic.
Even if we do not use the main microphone, the basic problem of the strong crosstalk and the delay will remain.
While this is a simple example, image the complex situation of a whole orchestra:
Above: Illustration by Gregor Zielinsky. Recording an Orchestra.
5 – Solutions – Which options are available?
Now that we have discussed the complexities of crosstalk and delays when we mic up an orchestra, we will have a closer look at how to handle this. Which options are available? Can we move closer to the instruments?
This will not lead to relevant improvements in terms of crosstalk. However, it will cause a strong decrease in sound quality. The compromise between crosstalk rejection and loss in quality is not satisfying.
This sounds as if multi microphone recordings would not be possible. But of course we know it is. And (usually) with great results. However, this is mainly based on channel based recordings and not so much with crossover material (repertoire), which is very difficult to record and mix.
Object based recording and software is much more complex. Software that is producing virtual headphone 3D sound, is working with a lot of „tricks“, in order to simulate the brain, that a sound source would appear outside the head somewhere in the room around you (phases, delay, filters and more).
These software simulations are usually based on the assumption of „stand alone“ objects. Meaning the single instruments, objects etc. should be recorded alone with no other sound interfering! This is kind of a „Conditio sine qua non“.
For any kind of object based recording or critical recording situation, we need a perfect compromise between crosstalk rejection and the highest possible sound quality.
Musical Aspects – especially for Live Situations
Using close and good sounding mics also has a strong musical aspect. You can make complex arrangements as if you were composing or arranging for a „normal“ orchestra score or studio situation.
Strings do not just need to perform just high notes. Viola, celli and double basses can be heard in a normal way. The orchestra will work and blend perfectly with the band.
REMIC MICROPHONES has developed string microphones for many years with the main goal of keeping sound quality in mind plus optimal crosstalk rejection. Therefore, the instrument specific REMICs deliver the prefect result, when it comes to the balance and compromise between sound quality and crosstalk rejection.
REMIC Microphone Types
Basically, REMIC MICROPHONES for strings are offered in two main versions:
1 – Studio/Live Version
The Studio/Live versions focus on a very high and natural sound quality combined with a high crosstalk rejection. The Studio/Live models have an omni-directional polar pattern.
2 – LB Live Version
The LB Live versions focus on a very high crosstalk suppression combined with a high sound quality, with slightly adapted frequency range. The LB Live microphone models have an angled figure of eight polar pattern. They are typically used for rock, pop and crossover repertoire and in productions with high sound pressure levels where isolation of each instrument is crucial.
Each version exists as unique version for each of the following string instruments:
- Double Bass / Upright Bass
There are also special versions for wireless transmitters from Sennheiser and Sure, they are called the WLM models and are made also in Studio/Live and LB Live microphone models.
You will find further information under these articles in the REMIC Academy section (“How to mic a ……”)