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Channel surfing the names of audio channels

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As an industry, we agree on many things. So why can’t we agree about the names of audio channels? Anthony Grimani reports.

We have developed languages, vocabulary and grammar so that we can communicate with each other on subjects that are as subtle as the flavours of fine wines. Meanwhile, our industry hasn’t agreed on how to name the channels of surround sound or immersive audio systems. How confusing!

After years of designing, installing, commissioning and servicing home cinema systems from entry level to the highest end, I have observed errors, mislabelling and misconnecting galore. Here is how I would like to see us all refer to the audio signals that travel from the surround processors, through the equalisers and amplifiers, and finally to the speakers. For a 9.1.4 channel system, I would see us using these names and acronym labels:

  • Left (L)
  • Centre (C)
  • Right (R)
  • Side left (Sl)
  • Side right (Sr)
  • Back left (Bl)
  • Back right (Br)
  • Wide left (Wl)
  • Wide right (Wr)
  • Top left 1 (Tl1)
  • Top right 1 (Tr1)
  • Top left 2 (Tl2)
  • Top right 2 (Tr2)
  • Subwoofer 1 (Sub1)
  • Subwoofer 2 (Sub2)
  • Subwoofer 3 (Sub3)
  • Subwoofer 4 (Sub4)

The Left, Centre and Right channels are the primary drivers of the sound system. They don’t really need the addition of an ‘F’ in front of them. In fact, that can cause confusion and make the cable labelling more challenging.

The Side channels are now ubiquitous in all 5.1, 7.1 and immersive formats. Their label being simply Sl and Sr prevent confusion with L and R and can also be interpreted as ‘Surround’ left and right. The ‘l’ for ‘left’ and ‘r’ for ‘right’ are in lower case. Using the label Ls or Rs, as some naming conventions do, can result in connection errors when someone doesn’t look far enough around the cable and plugs it to the Left or Right channel instead. That leads to a very exciting and active surround soundfield, but plainly wrong…

If your system has two or more pairs of Side speakers, you can label them Sl1, Sl2, Sr1, Sr2.

The Back channels are called Back in order to avoid using the word ‘Rear’. Why? Because Rear begins with ‘R’, resulting in a label of Rr for the Rear right channel; I have often seen cables that were labelled as such erroneously plugged into the Right channel. Once again, you may be very excited by how active this surround experience would be, but it’s just wrong…

The ‘l’ for ‘left’ and ‘r’ for ‘right’ are in lower case so that you can first and foremost see that the connections Bl and Br are for the Back channels. It’s fairly rare that anyone would clearly indentify the Back left and Back right being reversed in the soundtrack – although, of course, you want them properly laid out!

I’m also not a fan of the fairly common Lsr and Rsr designations for Back speakers, because they veer into alphabet soup territory.  I mean, really, what is a Left surround rear speaker?

Now what are those ‘Wide’ channels? These are the all-too-important speaker locations on the side walls, forward of the Side speakers, at about +/-45 degrees from your centre axis. These signals are created, coded, and decoded to reproduce a clear and active front stage sound location that is outside the screen boundary. Sound mixers use these a lot in action movies, and they are very active in movie theatres. They fill in the sonic hole that is otherwise left open between the Front and Side speakers, which adds a surprising amount of realism to the soundfield. Dolby, DTS, and Auro aren’t doing a lot to publicise these, but the film sound mixers I talk to love using them. So, please, plan on placing a pair of good speakers (maybe only a bit smaller than the LCR) on the side walls. Call these Wl and Wr.

Now on to the Top speakers. Sometimes they are called Heights, but, in fact, there are some subtleties here. Those formats that place added speakers on the walls above the existing Front or Side channels usually call them Height speakers. So to be clear about what is actually on the ceiling, let’s all call these Top speakers. Simply Top left (Tl) and Top right (Tr) will work. If you are using four Top speakers, go for Tl1, Tr1, Tl2, Tr2, where 1 and 2 refer to the forward and backward areas. Trying to write the words ‘Top Front Left’ onto the labels is just too long and will potentially cause a connection error to the real Front channels!

And, finally, about the subwoofer…you may notice that I showed four of them, while referring to the system as a ‘.1’ channel scheme. There should be four subwoofers in any good quality home cinema in order to improve the bass uniformity throughout the room by eliminating standing wave gain. Much research has shown that this works better than single or dual subwoofer solutions, with the best overall results coming from one subwoofer in each corner of the room. Ideally, you also set their delay, level and equalization independently using a digital signal processor. You can add some precision by labelling these SubFl, SubFr, SubBl, SubBr for the four corners if you want, but beware of that alphabet soup! Some formats or surround sound processors actually generate 2, 3, or 4 different subwoofer signals for the front, side, and back areas of the room, and these would correctly be called a ‘.2’, ‘.3’, or ‘.4’ scheme. These approaches aren’t useful in small room applications where we need to work hard to eliminate standing waves; they only come in handy in large commercial cinemas – and marginally at that.

With clear and consistent labelling of all the channels in an immersive audio system, you will save time and money by avoiding connection errors and significant debugging. Just teach your team the above channel labels, and make sure they stick to them (pun intended).

 

Chase Walton contributed to this column.

About Anthony Grimani

Anthony Grimani

Anthony Grimani is president of PMI, Ltd., a home cinema engineering firm, and MSR Acoustics, a manufacturer of fine acoustical tuning systems. MSR is represented in Australia by Wavetrain (www.wavetrain.com.au).

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