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Audio Troubleshooting

For Experts Only

If there is noise, distortion, or imbalancing in any room, an audio-visual expert should be called in for assistance. An audio-visual expert is someone who has volunteered for SCALE for many years, and has experience setting audio-levels for both the room and the monitor feeds. The following procedure is for the experts.

  1. Identify the primary issue in the room. What needs to be fixed? Audio issues differ in the proper fix, and so a clear understanding of the issue before doing any workis important and prevents further errors. Possible errors include:

    1. Hum or buzz. There are generally two causes of constant hum/buzzing. Ground loop buzzing (60Hz buzz) is caused by audio equipment being grounded to different grounds in the facility. With multi-phase power this is easy to do. Possible solutions: connect equipment to the same ground (same electrical outlet); push the ground-lift switch on the DI Box <insert picture here>. Sometimes the issue could also be caused by poor shielding of the audio cable. First check to see that the audio cable is not crossing near any power cables, as this might be causing some of the hum. Additionally, look in the room for any malfunctioning fluorescent lights.

    2. Distortion. Distortion is caused when signals are amplified too much. This often means gains are too high.Possible solutions: Before performing adjustments to the gains, check with AV NOC to ensure that there is distortion on the AV monitoring feed. If distortion is detected on the monitoring feed, Adjust the mixer board to bring down the gains. If distortion is not detected on the monitoring feed, do not adjust the gains, but reduce the volume knobs. See noise (iii)

    3. Noise. General noise is a more difficult problem, but can be the result of amplifying the output to the speaker too high. Is the noise constant or intermittent? Possible solutions: If the noise is intermittent, the cable might be damaged. Follow the cable’s path and look to see if maybe the cable is/was being crushed by a chair or table leg or was laid down and bent at too narrow of an angle. In addition, check that connections between cables and equipment are secure.

    4. Feedback. Feedback is the unintended “infinite loop” of amplification of a sound and can occur when a microphone is pointed toward a loudspeaker and the amplification is set too high. Solving this problem has two aspects: triage and solution. When it immediately happens, the sound is deafening to the audience, so your instinctual reaction should be to lower the master faders to stop the feedback. Once you’ve lowered the sound, then you can begin to think about how to prevent it. If this is a panel with multiple microphones, turn off unused microphones. The more microphones that are hot, the more likely feedback is to occur. Is one presenter standing near a loudspeaker? Turn down their gain.Note: before adjusting gains, please consult with AV NOC.

  3. Identify the affected portion of the audio system. Problems with audio equipment can appear anywhere in the chain of the audio system. Once the affected portion is identified, work can focus there to resolve the issue, before expanding into other portions. This can keep the amount of work minimal. Parts of the audio system:

    1. Single loudspeaker. If a problem affects one speaker and not the other then the problem is often with the built-in amplification in that speaker. Look there first. Is it turned on? Next, check the cables.

    2. All loudspeakers. If a problem exists in multiple speakers,but notthe monitoring feed, the problem might be with the in-room audio mixer settings. Check to make sure the channels are not muted and that the channels and mix settings are appropriately set. Note:The monitoring feed is post-gain controls and thus these should not be adjusted unless the monitoring feed is also affected.

    3. Monitoring feed. If a problem is reported on the monitoring feed, but is not apparent in the room, then the output settings to the monitoring feed are at fault. Confirm that the appropriate channels from the in-room audio mixer are being fed to the networked audio mixer. In addition, gains can be checked for this issue.

    4. Inputs. If the problem is observed in both the monitoring feed, and the room, the problem likely exists with the inputs. Adjust there first. These include the gain settings.

  5. Perform adjustments. Adjust the system to fix the above isolated problem, and perform the adjustments for the affected part of the system first. Remember, settings dialed far past unity gain (labeled “U” or “+0db” on most systems) are often likely to be contributing to the problem.

  6. Rebalance. Once the issue is solved, the other affected settings should be adjusted as minimally as possible to ensure that the room still operates normally. Move along the chain of settings from the inputs to outputs.

  7. Re-test.

Things to keep in mind:

  1. One debugger at a time. Only one individual should be touching settings at a given time. Far too much time has been lost in past years when 2 debuggers are adjusting 2 settings at 1 time. If another volunteer has a suggestion, formally hand-off ownership of the debug.

  2. Be procedural. Work an area of the system from input to output.Don’t just randomly adjust settings.

  3. Fix one setting at a time. As much as possible, fix a setting, test it independently (with headphones) and then move on to the next setting. Varying 2 settings at once is usually a bad idea.

  4. Minimal changes are best. Keep adjustments small, and line levels low but sufficient to do the job.

  5. Unity gain is good. Going far past unity usually should be reasoned through as it often causes the aforementioned problems.