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Testing an AG's Sound

 Simple methods to test and improve the quality of AG audio.

 

Introduction

One of the most important aspects of the Access Grid experience is Audio Quality.

As mentioned in the introduction, many node operators are oblivious to the quality of their own audio transmission. This section of the guide demonstrates simple methods and tests to fine-tune the audio quality of your AG.

Audio Problems

There are a number of audio problems that can exist within an Access Grid. These include, but are not limited to, the following:

  • Audio levels too low
  • Over-driven (hot) audio
  • Poor echo cancelling
  • Annoying ambient noise
  • Fluctuation of audio levels
  • Speech being truncated

Watching the Rat Meter

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One of the most basic test of your audio is to watch the talk meter in "RAT". When talking in a normal speaking voice, the LED's in RAT should peak in the orange region. If the meter levels light up fully, the audio is over-driven and the gain for the input needs to be lowered. If the maximum level only lights a few green LEDs, the audio pick-up is too low and needs to be increased. Finally, with no one speaking, any fluctuations of the meter levels are likely to indicate ambient room noise that should be eliminated.

The meter level in the RAT below is too low. These audio levels need to be increased.

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The meter level for RAT below is too high and will cause the audio to be over-driven. This node needs to decrease microphone levels.

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The level on the RAT meter below is nicely balanced - it demonstrates a good audio level for normal speech.

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Using a Portable AG Node to Test your AG Node

One of the best methods of testing your Access Grid is to monitor the audio with a portable Access Grid node. With a set of head-phones connected to the portable "virtual" node, you will be able to hear your audio exactly as it sounds to remote participants. You will be able to detect if your audio is set too low or being over-driven, whether any ambient sound is being detected and if any audio fluctuation occurs.

This method of testing is extremely effective, as you are able to hear the effect of any change made to the gain levels, input devices or RAT settings instantaneously. The disadvantage of this method is that you need a portable AG to conduct this test.

Using a Packet Reflector to Test your AG Node

Description

AudioReflector is a simple program which listens on a multicast address and port and reflects all valid RTP packets back with a certain delay. The reflected packets are modified (their SSRCs are changed) to enable them to show up as separate sources in other RTP applications, in particular RAT. When this program is running in an Access Grid Venue, you can test your audio by simply going to that Venue, talking into your microphone and verifying that the audio is played back to you with a certain delay.

Using the Audio Reflector as a simple test

  1. Start the VenueClient

  2. Go to the Audio Reflector Venue. This is achieved by:
    • Going to the APAG Lobby (AG 3 https://vv3.ap-accessgrid.org:8000/Venues/default) [AG 2 https://vv2.ap-accessgrid.org:8000/Venues/default]

    • Going to the Service Lobby

    • Going to the Audio Reflector Venue

  3. Once in the Audio Reflector Venue, RAT should show (after a small delay) three audio sources. Your own name or node name should appear twice, and there should be an AudioReflector source as shown in the RAT screen capture below.

  4. Ensure that both the Talk and Listen checkboxes are selected in the RAT user interface.

  5. Talk briefly into a microphone.

  6. A few seconds later, the reflected audio should be heard. The reflected audio will help you identify how your transmitted audio sounds and if your audio is being overdriven or if any echo canceller problems exist. 

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It should be noted that if other people are present in the Audio Reflector venue, you will hear both their source audio and their reflected audio. In this case you can either mute all other node sources using the Rat user interface or simply wait until the other participants leave.

Using the Audio Reflector to perform advanced tests

Assuming you can hear your reflected audio after some delay, the next step is to use the "Shared Application" to adjust the delay and play test sounds. This can be used to further check the audio performance and confirm that the echo cancellation is working acceptably. First you'll need to download and install the Shared Application. This should be available in the AudioReflector venue, but if not it is available at:

http://sheriff.anu.edu.au/~rhys/AudioReflector/downloads.html

Install the shared application using agpm.py:

agpm.py -z AudioReflectorController.zip

You will have to restart the VenueClient to use this newly installed Shared Application. Once the VenueClient is restarted and it is in the Audio Reflector venue, select the Venue menu, then Start Application Session, then AudioReflectorController. You should then have an AudioReflectorController instance under the Application Sessions item in the list on the right hand side of the VenueClient window. Double click this item, and after a short delay, the Controller application should appear similar to the image below.

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The Audio Reflector Controller user interface is split into 3 parts, the top section consists of a slider and an Apply button. If the controller successfully contacted the AudioReflector server, then the slider will show the current delay in seconds for reflections. The middle section shows a list of test sounds that are available to play back and the Play button. At the bottom of the user interface, there is a status log that can be used to ensure that the Controller application is successfully communicating with the AudioReflector service. On startup of the controller application, the Status log should show something similar to the following text:

01/06/2005 13:44:45 : Started
01/06/2005 13:44:45 : Server return version 0.1.0
01/06/2005 13:44:45 : Got delay of 3000 ms from server
01/06/2005 13:44:45 : There are 2 test sounds, populating list:
01/06/2005 13:44:45 : Got test sound name "cookoo.wav"
01/06/2005 13:44:45 : Got test sound name "test.wav"

If what you see is something such as the following, then you should contact us and report the problem as this might indicate that the AudioReflector service has crashed.

01/06/2005 14:18:56 : Started
01/06/2005 14:18:56 : Failed contacting server (socket.error:(111, 'Connection refused'))

Finally, there are 2 buttons down the bottom of the user interface. The Refresh button queries the service again for the current configured reflection delay and the current list of test sounds available. The Exit button closes the SharedApplication.

Use the following steps to further test your audio setup:

  1. Adjust the Reflection Delay to 5 seconds and press the Apply button, and verify that the following message is shown in the Status log: 01/06/2005 14:27:46 : Set delay to 5000 ms

  2. Select a Test Sound and press the play button. You should hear the test sound almost immediately

  3. Maintain silence for 5 seconds after the test sound is initially heard and listen for an echo of the original sound. If no faint echo is heard then your echo cancellation is working well.

Attending Testing Sessions or Testing with other Nodes

Once you've checked your audio using one of the above techniques, the real test is to participate in testing sessions with other Access Grids. This could simply mean that you attend a regular AG testing session run by your local region, or alternatively with a couple of other AG’s as an ad hoc testing session. It is recommended that you conduct testing sessions with more than one location - as a third opinion is always beneficial - and just in case the AG you are testing has audio problems of their own.

Testing sessions are highly recommended. Many of the people attending the sessions have extensive AG experience and may be able to identify problems and offer possible solutions.

Prior to the testing session proper, it is a good idea to self-check your audio using the “Rat” meter level. This will save the time of node operators at other Access Grid locations.

Room Design

There are many variables that can influence the audio quality within an Access Grid room. One of these variables is the room design and layout.

Having properly positioned microphones and speakers can substantially improve your audio.

Microphone Placement

Ensure that you have enough microphones placed throughout your Access Grid so that participants can be heard clearly without having to move microphones every time a different participant speaks.

We will not get into the argument that ceiling microphones are better or worse than desktop microphones, but the following list details some of the advantages and disadvantages on the placement of microphones for you to consider.

  • Desktop microphones – Great for presentations as they are generally close to the main presenters which gives greater depth to the quality of the speaker’s voice. The only disadvantage of this is that desktop mounted mic’s generally have a limited pickup range.

  • Ceiling mounted microphones – Great for picking up audience participants and allowing people throughout the room to be heard. Ceiling mounted microphones, if configured correctly, can enhance the audio of an Access Grid and allow everyone to be heard. Unfortunately this benefit does come at a cost, namely that ceiling mics require more tuning. They are generally further away from the speakers, thereby requiring their gain levels to be set at a higher level, which can also introduce complications such as additional ambient noise. Another thing to watch for is that due to the relatively large distance between the participants and microphones, voices may sound distant or hollow.

  • Radio microphones – Radio microphones are great when the presentation is being shared around multiple speakers. Lapel radio mics are also good for presenters who require greater mobility. Radio mics are also beneficial in large rooms that contain a large audience; here, the microphone can be passed to participants at the back where desktop or ceiling mics cannot hear the conversation. One thing to consider when using radio mics is that the process of passing a mic from speaker to speaker is an impediment to interactivity if the person wishing to speak has to wait until he or she receives the mic.

Each of the microphone types listed above has their place within an Access Grid. The use of a single microphone type makes setup and echo cancelling simpler, however it doesn't provide the range of options that would be available with multiple microphones.

Speaker Placement

The placement of speakers is also an important aspect of Access Grid audio. Wall mounted speakers provide the feeling that the audio is coming from the direction of the Grid Wall, but can experience difficulties associated with sound reflection from the rear walls. Placing speakers too close to microphones also poses difficulties for the echo canceller. When these circumstances are unavoidable, one possible option is the use of sound-insulated curtains.

Problems and Possible Solutions

Audio Too Low

Try increasing the gain levels on your inputs. This can generally be done by increasing the gain levels on “Rat”, through the mixer on your operating system and/or the input levels on the audio mixer/echo canceller device.

Audio Too Low

Changing the gain levels in RAT may not have the desired effect for some users. To check, move the talk slider in RAT and watch the alsamixer window and see which level moves. The “alsamixer” does dynamic updates so you should see the alsamixer window change when you move the RAT slider.

Note that it does not work the other way around - ie. RAT does not do dynamic updates if you change the levels in alsamixer.

The level of line while moving the slider should NOT move. Instead, the entry with "CAPTURE" above it should move. If your input is mic, then you should be right, but it's worth checking.

The solution :

Add the following line to the $HOME/.AccessGrid/local_services/AudioService/rat file,

export OSS_IS_AC97=1

just above the line that reads

exec rat-4.2.2 $*

After you restart your VenueClient, the slider should change to the correct setting.

Audio Over-Driven (Audio Hot)

Try decreasing the gain levels on your inputs. This can generally be done by lowering the gain levels on “Rat”, through the mixer on your operating system and/or the input levels on the audio mixer/echo canceller device.

Poor Audio Quality

There are a number of reasons why your audio quality is poor: * Audio sound distant or sounds like it has a “Tube” effect. Unfortunately, even with the best quality of microphones, the closer they are to the source, the better the sound quality will be. Try placing the microphone close to the audio source and lowering the gain levels and see if that makes any improvements.

Poor Echo Cancelling

This problem generally reflects poor configuration of your Echo Canceller device. Depending on the device you are using (i.e. Clearone (XAP400) or Polycom(Vortex)) it is best to consult the user manual for your particular device or alternatively consult your audio/visual technicians.

Some other simple things that may help with removing any echo problems include:

  • Turning down the output volume;

  • Moving microphones away from speakers; or

  • Reducing the gain of your input devices.

It is critical that your Access Grid doesn't produce any echo, otherwise other Access Grids will have difficulty in conferencing with you.

Poor Ambient Noise

There are a number of variables that can affect the amount of ambient noise detected. The best thing initially is to try and remove as much ambient noise from the room before attempting to adjust any audio settings.

Things such as air-conditioning, noisy computer workstations and external noise can give off a fair bit of ambient noise which can be picked up by the audio pickup devices.

Some other simple things to consider that may help with removing any ambient noise include:

  • Placement of the microphones can significantly affect how much ambient noise can be detected. An example of this is placing them near air-conditioning vents which generally causes wind/blowing sounds to be detected;

  • Placing AG nodes into an enclosed rack may help to reduce the noise output of the computer workstations; and

  • Using sound insulation curtains may help to remove any external sounds that may exist.

Once most of the simple adjustments have been made and tested, additional configurations to gain, mixer and other audio settings can be made.

Generally speaking, by lowering the gain levels on the input devices, this will reduce any ambient noise pick-up. Be sure that you don’t lower it so much that the speaker’s voice is reduced to an unacceptably low level.

Audio Fluctuation

Another audio problem that can be hard to identify for an Access Grid is audio fluctuation. A perfect example of this is when the audio volume fluctuates from being too loud to being too soft without any user interference with the audio settings.

One of the best methods to determine if you have any audio fluctuation is to read a number of paragraphs and listen / watch the RAT levels to determine whether any of the transmission levels are changing. One example of where this problem has occurred is when an AG session with a particular AG - their initial audio always sounded very good, but over the duration of 20 or so minutes, the volume would decrease to an unacceptable level which made it very difficult to hear.

If you experience any audio fluctuations, it is advisable to investigate your echo canceller/mixer device. Again it is recommended that you consult the user manual for your particular device or alternatively consult your audio/visual technicians.

Speech being Truncated

Another audio problem that may exist within Access Grids, is the problem of audio being clipped. Generally this occurs at the beginning and end of when someone is talking where the first and last words are truncated.

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A well known cause of this problem is if the Silence Suppression setting found within the RAT audio preferences is turn on. It is recommended that this feature within RAT be disabled as displayed in the image above.

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