Skip to Content

Tag Archives: Audio Quality

What You Should Know About “Microphone Gain Structure”

When it comes to echo cancellation, microphone gain structure is essential to your success.

Let’s face it. When you break down today’s digital signal processors for audio and video conferencing, all you really have is a metal box with a little green guy inside running faders up and down. Although you tell him things like why, when, and how fast to perform his duties, he’s still relying on you 100% to accurately set up your microphones, otherwise known as the ‘front end’.

 

After working in this industry for over 16 years and programing many echo cancelled DSP mixers, I’ve seen that nine out of ten issues are due to the same cause.  Our little green friend (let’s call him Simon) is usually sampling incorrect information  due to the gain structure not being set properly on the microphone input. When this happens, you’ll see what could be referred to as a “domino effect.”  Although Simon won’t admit it, our friend is nothing more than a piece of electronics that can, and will, make mistakes.  However, when he is receiving the correct information, the number of mistakes he makes is reduced dramatically.

 

Think of it as if you were an individual who needs to wear glasses to see properly. You drive down the road wearing your glasses, and everything seems fine. Sure, you could have an accident at any time; but the odds are typically slim. Now pull over, take off the corrective lenses you love wearing so much, head on down that open highway, and see what happens. Just as we aim for 20/20 vision with our eyes, in our industry, we also aim for a standard volume level that the average talker uses when speaking.

 

Believe it or not, the average person speaks right around the 64db mark at a one-meter distance. Now, this isn’t like your average parent, at home with three misbehaving little ones, trying to deal with them after a long day of work. This speaking level is more like the average person talking normally during a casual conversation.  Understanding this level will help you tremendously with your setup.

 

Here are a few tips and procedures to follow to keep in mind while setting up your microphones for conferencing.

 

Have the proper tools:

 

Although most people will simply use speech as their source, and watch the meters within the applied software package, I’ll briefly run through another method that is arguably more accurate.

Speaking is 64db

 

We mentioned earlier that the average talker speaks at 64db at a one-meter distance, and we know that in almost every echo-cancelled DSP we want to see 0db from the signal being picked up by the microphone and reflected on the input. Using our signal generator, we can measure one meter away from the microphone element and place the generator there. Turn the signal on and set it for pink noise. We use pink noise for this process, as pink noise has equal energy per octave. Using your SPL meter, adjust the level of the noise to be 64db at the microphone. Now we are simulating speech, and can set our input levels accordingly to peak at 0db.

 

Regardless of what DSP you choose for your echo cancellation and mixing, setting your inputs peak at 0db using the method above will ensure Simon has the correct information to sample. When Simon is happy, everything works perfectly.

 

Today’s digital signal processors for audio and video are so advanced that I ask the question, in your experience regardless of most other settings, when your inputs are set properly, doesn’t your audio system sound pretty good?

 

 

EFFECTIVE AUDIO FOR VIDEO CONFERENCING – Part Two


 
This post continues our discussion on addressing what needs to be done with audio to make it effective in all situations so users can clearly hear everyone involved in audio and video conferencing calls.
 

Audio Is The Foundation

 
Humans can tolerate visual interference – a grainy image, untrue colors, and jerky images. But, the audio must be high quality in order for listeners to perceive the words. Decades of research have shown how specific types of signal degradation affect perception. This research has been used to produce telecommunications networks that are optimized for transmission of high quality human speech.
 
One study, conducted by TRI, had 100 participants view video and evaluate the quality of the image as they thought the bandwidth of the video was being altered. In reality, the bandwidth allotted to audio was changed. The participants perceived the video improving as the audio improved, even though no changes were made to the video quality.
 
Audio must be high quality in order for people to perceive the words. Speech can tolerate some clipping or the loss of an occasional syllable, but time lag is intolerable to listeners during conversation. When the range in the voice is muffled and speaker identity and intelligibility are affected, calls are no longer understandable. All these factors make audio quality an extremely important component of a video conference. Lowered speech intelligibility will inevitably obscure natural communication, take focus away from important aspects of the meeting, and cause fatigue.
 
The way audio is handled in a video call can also be an issue. The quality of speech transmitted over a local area network (LAN) or wide area network (WAN) can be impacted by the way audio packets are handled. Compression and decompression of audio is a standard part of a video conferencing system, and can be a source of reduction in audio quality. Complete loss of some audio packets during transmission over the pubic Internet may also occur. As a result, the audio signal may suffer in quality and delay. In some instances, to optimize audio in a video conference, a full duplex voice telephone circuit is used to carry the audio portion of the conference. The independent channel can also be helpful for troubleshooting if participants have difficulty with the LAN or collaboration applications during a meeting. As an alternative, a company can pay a service provider with Quality of Service (QoS) technologies like Multiprotocol Label Switching (MPLS) and Differentiated Services or DiffServ, which allow audio and video data to be transmitted with a guaranteed level of quality.
 

Achieving Audio Quality

 
The goal in any video conference is for the participants to feel they are in a meeting room with good acoustics and do not feel distracted when others whisper, tap pens or rustle papers. If a room is properly equipped and designed, meeting participants should not have to worry where they sit or stand in order to be heard. They should feel as if everyone is in the same room, even when communicating from a distance. Achieving quality audio is dependent on both the right equipment and the proper environment.
 

 
Room design is an important component for quality audio. A room with hard surfaces everywhere results in too much echo. When setting up a room for a video conference, consideration must be given to whether there are reflective surfaces near the microphones and speakers, whether there are sources of noise coming from other equipment or SS systems, and how well the room is sound-insulated from adjoining rooms. For some rooms, a premium or installed audio system may be appropriate.
 
Check for symptoms of bad acoustics by clapping your hands. If it sounds like you are in an empty barrel, garage or basement, you need acoustical treatment of the room. Your goal is to achieve a sound that is relaxing and inviting. The next step is to look at your meeting room and check for hard floors, hard walls and the presence of undraped windows. Hard surfaces are part of the cause of bad acoustics. The secret to making your room better for audio or video calls is to have soft surfaces that absorb sound. Carpeting, upholstered surfaces, and draperies are examples of how to soften a room to achieve better audio. But changing a room is not always practical or desired. A professionally installed system is designed by an integrator to mitigate noise and echo while optimizing desired sound.
 
Acoustical wall panels will also help achieve proper sound in a room. Never let two opposing walls remain without absorption. Acoustical treatment attenuates the reflected sound and increases the usable distance between sound sources and receivers. This will increase the audio quality over a wider seating area.

 
ClearOne’s new Beamforming Microphone Array automatically configures to room acoustics with twenty-four microphone elements, steering its pickup pattern towards participants in the room and rejecting unwanted noise and reflections.
 
Many systems today use simple microphones with little directional sensitivity. While these microphones capture sound from all directions, they do not adequately suppress ambient noise. New microphones are being developed to optimize directional sensitivity. Installing the right audio equipment and treating the room will help optimize audio quality.
 
This process does not have to be expensive. One end user solved the audio problems in a room located in a parking garage inexpensively by hanging lined draperies on the wall. The small changes worked and resulted in acceptable audio during a video conference. Small adjustments to the room can make slight audio improvements, while solutions ranging from speakerphones to professionally installed systems can bring the greatest improvements to conferencing sound.
 
Finally, there is no substitute for proper speech etiquette. Anyone speaking should use a normal speaking voice, with no need to shout or whisper, and always direct his or her voice at a microphone. The right audio system, with intelligence provided to automatically correct microphone gain without causing unnecessary pumping noise, is the approach to take for optimized audio. With intelligent systems presenters are able to stand or walk around a room without being tied to a lavaliere microphone or having to directly speak into a microphone.
 
Awareness of what needs to be done to achieve good quality audio is the key to video conferencing success. Good audio solutions for every conferencing application – with or without video – are important to successful calls.
 
S. Ann Earon, Ph.D., is president of Telemanagement Resources International Inc. and Founding Chairperson of IMCCA, the non-profit industry association for collaborative conferencing. She can be reached via email at annearon@aol.com.