Noise Kills Tele/Presence - Multi-Part Presentation

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Noise Kills Tele/Presence - Multi-Part Presentation - Top-10 Tele/Presence Design Tips - Part 1 - Introduction to Tele/Presence Audio

Remember like the adage, "It's the economy stupid. In tele/presence, "it's not audio, its noise."

There are many kinds of noise, echo (discussed in the future), machine noise, static and others. Noise drives us nuts, ruins meetings and even kills. According to TopicPulse.com, "More than 600,000 potential years of healthy life are lost in Europe each year due to noise-related death and disability, New Scientist magazine reported. Traffic noise alone may account for 3% of deaths from heart attacks and strokes in Europe. Chronic night-time exposure to noise levels of 50 decibels or above was enough to cause cardiovascular problems." Meanwhile, here in the U.S, OSHA regulations state that sound exposure limits before permanent hearing loss is as little as one hour at 100 dB (eight hours at 90 dB). In tele/presence terms, excessive noise can kill the meeting.
Now back to the point of this work - This article is not about outbound voice microphones or inroom audio speakers which will be presented at a later date. This is a multi-part brief introduction, not an indepth analysis on room design and network audio.
Design Tip #1 - Get tele/presence smart and select a location in the building that is quiet to begin with. The most effective and least costly way to isolate the room acoustically is to choose a quiet location in the first place. Interior locations that are distant from coffee kitchens, drinking fountains, vending machines, elevator shafts, fluorescent lighting, lavatories, and fan rooms are most desirable in terms of controlling for noise. Understand that these devices generate an enormous amount of noise which can cause "crosstalk" interference with CAT5/6 cable. Ambient noise coming from outside traffic, ringing telephones, public address systems, among a multitude of other possible sources, can be blocked by soundproofing the walls or double glazing the windows with noise-reduction curtains. Acoustic treatment need not be expensive and can include simple techniques such as carpeting the room and placing screens or wall hangings in appropriate places throughout the room to reduce echoing. Internal sources of noise, such as noise generated by the audiographic equipment, can be controlled by placing equipment in sound-proof cabinets or in another room adjacent to the teleconferencing room.
Design Tip #2 - Get Noise Smart - in other words, know everything about noise and sounds. As you read in the last issue of the TPF Newsletter, the human hearing range is 20-20,000 Hz but in practical terms, 80-7,000 Hz is an effective range for tele/presence applications. Click here for an indepth report from Cisco on voice fundaments or there are many useful tutorials in TECHtionary.com.
http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/phones/ps379/ps8537/prod_white_paper0900aecd806fa57a.html
Shown in green is the typical human voice range 80-11,000 Hz, however the typical or practical range is 300-6,000 Hz. G.711 is based on the industry standard of 300-3,400 where more human communications can occur while minimizing the amount of bandwidth transmission. Higher frequency ranges are desired for complex pronunciations like P-T, M-N, S-F as well as a greater user experience. G.722 provides high-fidelity audio 150-7,000 Hz samples.
For example, ambient noise is reference sound level or average room noise level. To measure the ambient noise, get a device to measure SPL-sound pressure level and measure noise/sounds often. SPL measures are taken with respect to the minimum threshold for human hearing. A 20 dB difference in SPL represents a ratio of ten-to-one in sound pressure. For example, 40dB SPL would be a SPL-sound pressure level that is 100 times greater than the sound pressure level of the quietest sound that normal human hearing can detect. If you would like to test your own hearing go here: http://www.freehearingtest.com/test.shtml

170 dB = rifle fire at 1m
160 dB = personal protection air horn
150 dB = rock music
140 dB = firearms (which go even higher), jet engine
130 dB = jackhammer
120 dB = car stereo, band practice, threshold of pain
110 dB = manufacturing machines, rock music
100 dB = chain saw, drills, car horns, motorcycle
90 dB = lawnmower, shop tools, truck traffic, city subway, construction machinery
80 dB = inside sports car at high speed, outside busy street, alarm clock, telephone dial tone
70 dB = vacuum cleaner,
60 dB = human speech, conversation
50 dB = open office background level, dishwasher in next room
40 dB = maximum recommended background room noise level for tele/presence room
30 dB = soft whisper
20 dB = quiet interior house
10 dB = normal human breathing
0 dB = silence

SN or SNR-Signal-to-Noise or CNR-Carrier-to-Noise ratio is the difference between the signal also known as carrier or carrier wave and noise. The SPL of human voice is 60dB to 70dB. If you get an SPL meter you can test various sound conditions such as watching television, working, coffee shops, etc. In practical terms, according to Cisco's TelePresence Fundamentals book (ISBN-1-58705-593-7), "Because of the way the human ear and brain work, background sound that is 25dB to 30dB less than human speech generally goes unnoticed. In other words, the carrier/signal should be 60-70 dB and the background should be less than approximately 35dB. Noise levels exceeding 42dB are cause for concern, and levels exceeding 50dB can cause significant problems with the tele/presence experience."

Design Tip #3 - Get SPL-Sound Pressure Level meters/tools - I own the RadioShack Digital Display SPL and like the digital display, ease-of-use and value but would like below 50 dB measurements. Search for a SPL meter that meets your needs as they can be expensive but when you consider the investment in the room a very paltry sum. If you have an iPhone, you can get a number of different audio applications including a SPL meter, you can carry with you everywhere. There are many ways to use the SPL meter. First, the A-weighted test analyzes "noise" level 500-10,000 Hz the total range and the C-weighted 32-10,000 Hz is for music.

According to Cisco's TelePresence Fundamentals book, "Within each of the six zones, the ambient noise is measured with the decibel meter approximately 5 feet from the floor using a slow sweeping motion to capture the average SPL for that zone. These measurements are done using an A-weighted test (best SPL analysis for human ears). A seventh measurement is taken using a C-weighted (best SPL for all uses including music) test within the middle of the room (front of zone 5) to capture the C-weighted average SPL for the entire room. Note that the C-weighted target is approximately 52dB, compared to the A-weighted target of 36dB mentioned previously.

Here's the RED FLAG - "You should be concerned with any A-weighted measurements that exceed 36dB, a C-weighted measurement that exceeds 56dB, or any specific source such as HVAC vents that exceed 36dB at 3 feet (1 meter) distance from the source. For all these tests, you should choose a time of the day that represents the high average, ideally, when the HVAC is actively producing air flow through the vents." Measure the lighting system as well. These SPL tests should be conducted during the day at random intervals.

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Reverberation is essentially a measurement of how long a sound continues to bounce around the room before decaying to the point that it can no longer be heard. The measurement used to denote reverberation is called RT60, which is a measurement of the time required for a sound to decay by 60dB.

Design Tip #4 - It's not from the room but from outside the room. In designing an audio or video tele/presence room is more about keeping outside noises from entering the room anytime. That is, it may be quiet at the moment but jet planes landing every hour or less cause the ambient noise to cause interference in the meeting. In addition to controlling for ambient noise, the tele/conferencing room should minimize reverberation. This can be accomplished if the walls are nonparallel and covered with noise-scattering and noise absorbing panels.

Design Tip #5 - test "under load." While it should be obvious but often not, as such it is separately and highlighted as a key Design Tip. Simply test and test often with different size groups and different discussion types.

Usage Tip #6 - Teach the users to minimize their own noise. Whispers, drumming on the table, paper shuffling—all will be transmitted. Confidential "side" conversations are picked up and transmitted. Place "Quiet" signs on the walls and on the tables to remind them. This also ensures effective user participation in the tele/presence meeting.

Design Tip #7 - Understand the voice telecommunications network being used. For example, discussed last week different voice CODECs provide different levels of audio quality. In addition, multiple channels are desirable for multi-screen implementations. For example, in the Cisco CTS-3000 system there are four separate audio channels; three wide-band ACC-LD-advanced audio coding low delay standard for 20 KiloHertz audio for mono and stereo and enhanced echo cancellation (discussed in next TPF Newsletter) and one G.711/G.722 channel for audio-only users or document/desktop sharing. Check with the provider to see what CODECs are supported, for example, G.711, G.722, G.722.1, G.722.1C, G.728, 64 bit & 128 bit MPEG4 AAC-LD are common to Cisco, Polycom and other providers. G.719 (licensed by Polycom) the wideband ITU-T standard is also available in many systems. There is an excellent though technical comparison of CODECs in Wikipedia - click here. http://en.wikipedia.org/wiki/Comparison_of_audio_codecs

SN or SNR-Signal-to-Noise or CNR-Carrier-to-Noise ratio is the difference between the signal also known as carrier or carrier wave and noise. SNR is measured in dBm-deciBel milliwatt. Since SNR is a ratio dB is referred to as 100 dB which would be a ratio of 100:1 (100 to 1). Zero (0) dBm equals one milliwatt. This is the same concept but dBm and dBA or dBa audio are different. dB(A) is used in sound volume or ear testing (70 normal to 130 pain level). A practical example of a high noise level is in LAN networks where noise from fluorescent lighting, soda machines, and other devices interferes with digital packet transmission causing packet loss (errors) and transmission is reduced forcing more packet re-transmission further reducing data throughput.

Design Tip #8 - Voice clipping, chopping or dipping occurs as the result of the VAD-Voice Activity Detector. VADs are used for silence suppression in packet voice systems, due to the need not to use bandwidth to send packets when there is no voice; think of this as not sending silence. VAD also reduces or suppresses echo suppression in echo cancellers. In addition, VADs are used to reduce room or background noise in IP phones, speakerphones and microphones. VAD systems determine the difference between human voice, tones, unvoice, "white noise" (similar in concept to white light (composed of equal amounts of all visible light frequencies) - a sound composed of an equal mix of all audible frequencies) and comfort noise (noise generated to let the user know the call has not been disconnected) and other sources. There are three or more types of noise or non-noise detectors: known energy level, adaptive energy level and spectral energy based on compression. Related to and part of VAD configuration is Comfort Noise or tone. Comfort Noise is the manufactured or artificial method of creating noise to alert the listener that the call has not been disconnected and/or the network is still operating. A human factor issue, comfort noise uses bandwidth to send nothing more than "white" noise.

Design Troubleshooting Tip #9 - Here are just a few of the common problems and potential solutions.
- Crackling and crosstalk – check for poor cable connections, cable network design and electrical grounding. - Static, hissing noise (white-constant, pink-less constant, brown-indescribable) – check the Voice Activity Detector (VAD). - Hum ("60 cycles AC-Alternating Current") – check wiring may be too close to electrical power sources, wiring and transformers such as lighting, water/soda/vending fountains. - Voice volume distortion of too loud, low, fuzzy, tinny – adjust or replace phoneset/softphone software.

Design Troubleshooting Tip #10 - Build a "shared FAQ" (e.g. SharePoint) online help system for other designers and users. Provide the means for users to submit their compliments/complaints to improve/fix problems. Encourage users to complete evaluation forms and contact users on a random basis to determine what they like/dislike. Tele/presence has failed on many occasions because system administrators assume users are satisfied when they "speak with their feet" by returning to their old ways.