Surround Sound 5.1

Surround sound 5.1 requires 6 speakers, being: 5 speakers and 1 subwoofer speaker.

The subwoofer is known as the LFE (Low-Frequency Enhancement) Channel.

The .1 at the end of the 5, means there is 1 channel going to the subwoofer speaker.

ITU Diagram for 5.1 surround setup

Speaker Placement in a room.

To the right is a basic diagram where to place the speakers for a 5.1 surround sounds system. This diagram also shows basically where you should be sitting to get the best representation (sweet spot) for listening and mixing for surround sound.

Subwoofer Theory.

The subwoofer is to bring out the low frequencies ranging from 3 – 120 Hz. The subwoofer is theoretically allocated one tenth of the frequency spectrum, even though they designed to cater for the 3 – 120 Hz, the human hearing can’t normally hear any frequencies below 20 Hz. This also depends if your hearing has been affected in any way. Generally, the subwoofer is used for effects or special occasions, e.g. a bomb blasting resulting in a rumble in the viewer's seat.

Audio engineers generally concentrate to bring out the 80 – 120 Hz frequency of the subwoofer to give the 5.1 surround sound.

Down below is a frequency chart that l can refer to, to give me a guideline for the bases of a 5.1 surround sound mixing.

The Centre Speaker

The centre speaker carries the main dialog of the story (peoples speaking) The centre speaker fills the gap of the phantom centre you get from the stereo system which is 2.0 (2 speakers). This centre speaker is the tip of the spare, it’s the speaker that controls the dialog and allows the listener to interact with what is happening on the screen. If the frequency isn’t correct, the listener will get frustrated when they are trying to follow the story. People who have hearing damage tend to lose the 3kHz frequency range of the frequency spectrum. So, keeping the centre speaker clear of other instruments if possible, will help the hearing impaired from getting frustrated. A couple of charts below is to consider when mixing surround sound, this is so that everyone can hear the film, concert or any other entertainment they are viewing.

Hearing chart interactor

Cookie bit hearing loss

Front side speakers (Front Left & Front Right)

The front 2 side speakers are basically the same as a stereo system, 2 sound channels for audio. When deciding to bring in the centre speaker, it is dependent on how you want to create audio representation as the viewer watches the screen. It’s important to also keep in mind that we naturally hear all our audio from the front of use (our head) than to the side and rear of our head. Visual and audio go hand in hand, as l think it is a big part of the human fight or flight psyche. Having the main content emerging through the front’s speakers (front sides & centre) will help the viewer get more involved with the entertainment. The trick is how to balance the ‘phantom’ centre which normally occurs with the 2 front side speakers comparative to a normal stereo system and the centre speaker from creating a ‘midrange bump’ from happening. The midrange bump can make the voice come across sounding harsh. What creates this problem is that phantom centre shifts when you move around the room and the centre speaker remains the same and alters the sound. (The centre speaker is mixed too loud)

It all depends on the depth of the centre speaker placement in the mix. I found a forum site that suggested there are two ways to approach and blending the audio:

1. keeping the dialog in the centre channel only like - Film and theatrical presentation

2. Using a mixture of phantom centre and centre speaker to give a modern stereo mixing

You can experiment with the depth of the centre speaker channel ranging from 10% to 85% to eliminate this midrange bump and help to give the desired aesthetic feel you want to create.

Divergence is the technical term for mixing the sound source through the 3 front speakers (Front Left, Centre and Front Right), Divergence gives the experience of an extended sound source.

The Rear Speakers (Back Left & Back Right)

The rear speakers are to create the sensation that the sounds are coming from anywhere horizontally (360 degrees) They usually put the atmos through the rear speakers, but once again it depends on how you want to sculpture your aesthetics to carry the visual on the screen in front. You now can have divergence on the back speakers to the front speakers.

Signal Flow

Check your audio DAW system settings are tick correctly.

The mixing and editing window now shows that all the track channels have 5.1 mixing capability and where the speakers are in each tracking channel. The mono output has one speaker window and the stereo output has two windows.

You can also create a stereo version from 5.1 downmixing or fold-down. I need to research this technique more, as it will create a quicker work-flow. The diagram below shows how Guy did his downmixing

The audio sound can now be shifted through different speakers to create an illusion while you watch the screen. Now you can get lost in an augmented reality world, while boring real-life continues outside your front door.

Surround sound has been around since the 1940s, but it’s with the advance of the DAW that has brought in the endless possibilities. You now have the ability to shift sound around in the DAW mixing suite and select what speaker you want to select, including what track and speaker channel.

To the right is a virtual console with a speaker selection window. The green dot indicates where you want the sound to be in the virtual speaker controller. So now you have total control over the speakers and audio placement. (It’s so exciting isn’t it.)

Every audio track can be allocated to a channel track. 5.1 surround sound has 6 channel tracks. Once I can afford to get this bit of kit, my audio world won’t be the same. The use of divergence though this matrix is a powerful tool in audio engineering. This is creativity in overdrive and the possibility of what you create is only limited to your imagination.

Conclusion

I’m only just touching the tip of the iceberg of 5.1 surround sound. I can see just how powerful this audio software is and also just how much there is left to learn. If I was to do a 5.1 project for the first time, I think I would approach it in this mindset at the moment to get through.

LFE – for special effects and I would keep as much as possible low-end frequency out of that area (to a bare minimum).

Front Speakers – The Dialog goes through the centre speaker (normally) and I would use the side speakers to deliver a broad spectrum of the audio, l would still have dialog coming out of the side speakers but l would use divergence (depth of centre) technique to control the mid-frequency bump and stop this from happening.

The Rear Speakers – Atmos and creating a feeling of depth in the sound, I would also experiment with front and rear speaker divergence.

Changing Speakers for Effect

I would experiment with a sound shifting from one speaker to another speaker, to give the impression of people and objects moving.

I think it is important to keep an ear out for frequencies during the mixing process, and to be sure that all the audio has a good clean quality about it, especially with the 3kHz for the dialog. People with hearing problems need 3kHz dialog frequency crystal clear so they don’t have to blast the rest of the family out of their chairs because the frequency dB level is too low.

Time to start saving the pennies for the augmented reality machine. Surround sound 5.1 is exactly the direction of audio engineering I want to be involved in. The side project that Phil and I are working in the last trimester could be our first surround sound project. We haven't had any time to work on it this trimester, but hopefully, we can in the next trimester. DRAC"S EMPIRE - Resurrection (a short animation musical.)

Reference

waves.com. (2017, December 14). Mixing in Surround: DOs and DON'Ts: Waves. Retrieved April 17, 2020, from https://www.waves.com/mixing-in-surround-do-and-dont

Silva, R. (2019, November 18). Do You Need A Center Channel Speaker For Surround Sound? Retrieved April 18, 2020, from https://www.lifewire.com/center-channel-speaker-4142693

Feinstein, S. (2016). Understanding Frequency Response - Why it Matters. Retrieved April 18, 2020, from https://www.alesis.com/kb/article/2227

Divergence - How do you use it? (n.d.). Retrieved April 18, 2020, from http://forums.musicplayer.com/ubbthreads.php/topics/1000934/Divergence_How_do_you_use_it

Farley, S. (2013, January 4). A Plug-in Vector Matrix. Retrieved April 18, 2020, from http://designingsound.org/2013/01/04/a-plug-in-vector-matrix/