Encoding Multi Channel Audio

By Phoenix

 

Velleman K8055
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Introduction

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Multichannel Audio

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Multi Channel Audio

NOTE

I’ve just dug up the sound mixing software and found it no longer works, there is now a new version that has a proper install engine and should now work, sorry for any inconvenience

Setup

I’ve had a few questions about surround sound from a PC, in order to get surround sound out of a PC you need three things

  1. Sound card (you can get 7.1 cards for £20)
  2. Amplifier/s
  3. Speakers

When you buy a 5.1 kit from PCWorld you are normally buying speakers and an amplifier, you will still need a 6 channel sound card (or 8 channels) to connect them to.

Cheap PC speakers come in two flavors, those with no power, be it battery or mains, and powered speakers.... unpowered speakers are no good, they really are the bottom feeders of the cheap spectrum.

If you have an 8 channel sound card you are fairly free on how you connect up your channels, for instance, you could connect 4 stereo speaker/amplifier kits, or as I have done a 5.1 and a stereo kit.... I hear by dub this the 2+5.1 setup.

The advantage of 2+5.1 is really cost, I can build such a system from fairly available hardware indeed most people already have a stereo system, and the price step of a 7.1 is a little steep, also its much cheaper to buy a high powered stereo set than a high powered 5.1 (or indeed 7.1)

When building such a setup to use channels singularly as below you don’t necessarily have to match kit, though there are a couple of recommendations

  1. Connect the stereo system to the Extra two speaker outputs, this way when you play true 5.1 sounds this will get managed primarily by the 5.1 system on the first 6 outputs.
  2. The stereo system often comes with an addition base speaker, no this doesn’t make a 2.1, its just a stereo with a woofer, base sound is non directional so it doesn’t matter if it comes from one or two speakers
  3. Splitting sound between the separate systems can have undesirable effects.
  4. Be aware of the extra base speaker on the stereo system its not controllable, it filters the base sound from the stereo signal and channels it to the central speaker, best use the two speakers in close-ish proximity to their bass speaker, or maybe if you want some extra kick to your sound system you could get a higher powered stereo pair and use them for loud feature sounds.
  5. the base speaker of the 5.1 is controllable, its the .1 channel

Encoding

The idea is simple, but to understand it you first have to understand the problem (which is also simple).

The problem with using a single PC to manage your sound output is that all the sounds will have to be played out of a single speaker system, which in most cases is a stereo system or maybe a 2.1, but you can easily rig a PC with a 7.1 surround sound system

However, we all know and love the wonders of 5.1 and 7.1 surround sound, I’ve got a pretty good 5.1 system in my lounge and when setup correctly with a good quality DVD the effects are mind-blowing... btw if you want to give your 5.1 system a proper test I recommend the opening sequence of Master and Commander where the ship is getting shot up, and the Star Wars episode 1 Pod racing sequence.

So, I found myself asking how difficult would it be to setup a multi channel sound system to only play each sound out of a specific 'feature speaker', this way you would embed a single speaker in each prop, and when you play that sound it would only come out of that specific speaker.

Surprisingly I found the answer, and its not only free, but easy to employ, with this method you can have up to 7 feature speakers (obviously you need a 7.1 system on your PC) and blend your sounds to any combination of speakers you like. NB, don’t bother trying to use the low frequency speaker as a feature speaker, low frequency sound is non directional.

Before you start download and setup the following files

Windows Media Encoder not critical but WMA files can be 12x smaller than AVI files

WavAviMux file and wrapper

In order to encode to a multi channel file you need to send a mono sound to each channel (speaker), which in the case of having the sound coming out of just the one speaker, and send a silent sound or mask to the others.

The problem with creating a mask is that it needs to be of the same duration and sampling rate of the original file (which must be mono) , fortunately there is a fairly easy way of doing this using Windows Sound Recorder

Converting your file to Mono

  1. Open Windows sound recorder (START, Programs, Accessories, Entertainment, Sound Recorder)
  2. Open the WAV file you want to encode in the sound encoder and check that the file plays back OK
  3. select File, Properties and note if the file is mono or not, and the bit rate.
  4. If the file is not mono select Convert Now, and select a mono format with the same bit rate as the current file
  5. Save the newly converted file.

Creating a Silent Mask

  1. Open Windows sound recorder (START, Programs, Accessories, Entertainment, Sound Recorder)
  2. Open the WAV file you want to encode in the sound encoder and check that the file plays back OK
  3. Decrease the volume of the file using (Effects, Decrease volume), each time you perform this it only decreases The volume by 25%, so you may have to do this a dozen times before you get silence, check the actual volume by playing the file, and make sure you have the Volume on your PC turned to max.
  4. When you have a silent file Save the file as a different name best use a name that links it to the original file i.e. Original_Silent_mask.WAV

Creating Sound File

Now you have your Mask you are ready to create your sound file

  1. Open the 7.1 sound program from your start menu, this program will simplify the creation of your file.
  2. Double click on the sound and silent mask boxes to select the sound files you prepared earlier.
  3. Double click on the fourth box to set the input filename and location.
  4. Select the number of channels you wish the sound to be played from.
  5. As you were making the above settings the command to encode the file will automatically be built in the command window.
  6.  If the command looks OK Click Make File
  7. Check the file looks OK

You should now have your multi channel sound file with your sound being played from just the one speaker, each time you play this file the sound will only come from the selected speaker, giving you directional sound

Your file should now be playable, however, you can improve the files size by using Windows media encoder to compress it, details on doing this can be found below (ignore the stuff about encoding, you’ve already done that)

Multi Channel Audio guide