6 Improvements for high quality teleconferencing

Transcription

1 6 Improvements for high quality teleconferencing 6.1 Staff allocations and roles High quality teleconferencing relies on constant attention to sound level and camera handling. We recommend allocating at least two staff members and more than three staff members for formal events. 1. Sound quality check and adjustment - Broken voice (input too high), sound level, advising microphone position, etc. 2. Camera handling - Video camera and Digital camera (for taking pictures) 3. Total management - Contact with other stations, presenter support, etc.

2 6.2 Ways of sharing PC presentation

3

4 6.3 Configuration for live demonstration (Surgery, Endoscopy etc.) Fig. 6.3 Configuration for live demonstration The Video mixer device is required for live demonstrations to switch between image sources. -Surgical view -Overhead view -Overview image taken by video camera

5 6.4 Types of microphone Microphones can be classified according to their features as follows. 1) The difference in methods of converting sound to electrical signal: Dynamic vs. Condenser Dynamic type: Signal conversion is the reverse mechanism of a loudspeaker. It has a simple structure and requires electrical power and a battery. Endures heavy duty and a high input volume level. Condenser type: This kind of microphone is usually used for small devices like PC headsets or wireless microphones. It requires a low voltage electrical power for its internal preamplifier. It has the advantage being small with a fine sound quality but has the disadvantage of resisting high volume input. Dynamic type Condenser type Electrical Required Not required power (Battery or plug-in power) Handling Robust Delicate compared to dynamic type Size Fairly large Can be downsized easily Intermediate (resists high sound Sensitive (prone to distort with loud Sensitivity input) input) 2) Difference in method of transmission: wired vs. wireless Both types of microphone have enough performance for teleconference with enough knowledge of features. Wired Wireless Price Reasonable(around $100) Expensive (few hundred dollars) Noise resistance Good Needs attention Receiving unit Not needed Needed Cabling Needed Not needed Some noise might be caused by the venue environment when using a wireless microphone. There are many possible reasons for this kind of noise, such as depleted battery, radio wave interference from nearby devices, crossed link with another unit, etc. A sound setup in which you can regularly check outgoing sound will raise awareness of this noise. 3) Microphone sound input: unidirectional vs. omnidirectional In general, vocal microphones are sensitive to sounds from only one direction because of their unidirectional feature. On the other hand, flat shaped microphones which are used for teleconferencing are designed as omnidirectional. Using these kinds of microphones with DVTS may cause echo (loop back).

6 We recommend using normal vocal microphones with a power switch for avoiding sound problems. 6.5 Handling detail of audio amplifier There are many kinds of audio amplifier products, and there can be many knobs for sound adjustment. Therefore, it can be difficult to handle these devices without knowledge or skill. This session explains the function of each knob and offers a sample configuration. We use the product MG102c (Yamaha co, Ltd.) as our example. Almost all deices provided by various companies have similar functions and knobs so this explanation should help you to handle your own device. 1) Input plug You should pay attention to not only the plug s shape but also the input signal power. The left picture shows two types of plugs; the upper side, named the XLR type, which accepts balanced sound signal, and lower side, named the TRS phone type, which accepts balanced or unbalanced signal (depending on the device). You can use either plug for short distance connection but if you want to connect from a longer distance (over 5 m), or if you hear some unexpected noise, it is better to use the XLR type. Each channel has an adequate sound level. For the microphone plug this is -40 to -50dBu. For the line plug this is -10dBu. If you want to set the input sound level to 0dBu, you have to amplify the microphone

7 input to one hundredfold and the line input to threefold. Therefore, if you connect a microphone to the line input plug, you can not get enough level of source from the amplifier because of inadequate sound power for the input plug. You have to connect the microphone into input plugs which have a GAIN knob. With regard to headsets (microphone) for use with PCs, almost all products use Plug-in powered microphone (condenser type) in them. It is not written clearly, but the microphone plug on PCs support plug-in powered device and supplies 1.5v electrical power. So if you connect this kind of microphone, it does not work well because of power supply. Phantom power supply is a similar function to that above but there is no compatibility between them. It should be used only as a guide to distinguish microphone types that are small and light weight. Mini-jack connector type devices should be plug-in powered. 2) Gain control Some devices describe this as TRIM. As mentioned above, sound levels are different among input signals. If you increase gain too much, it causes problems like distortion or loopback noise. Adequate adjustment is important for good sound. (The PEAK indicator lights only occasionally and briefly at the points of highest input.) 3) Equalizer The equalizer provides a boost or cut of up to 15db for 3 ranges of frequencies (HIGH 10 khz, MID 2.5 khz, LOW 100 Hz). However, this is not very useful for human voice, which only spans a frequency range of300 Hz to 3 khz. This function is usually used for music instruments of a certain frequency, for fine adjustments like removing minor noise etc. Removing the origin of a noise is the first choice for noise removal. 4) AUX Sends Used for output level adjustment of the AUX send channel. 5) PAN/BAL PAN: Determines the stereo positioning of the channel signal on the Stereo L and R buses. The center position sends the same sound level. BAL: Sets the balance between left and right channels. We can control transmission and reception signals separately with the PAN knob. 6) Level control

8 Adjust the level of each channel signal and the balance between the various channels. Knobs that are not in use are turned off to reduce noise. 7): Monitor output Outputs the signals adjusted by the MONITOR/PHONES control 8) Stereo out (Main out) Outputs the signals adjusted by the STEREO Master control. 9) AUX sends plug Outputs the signal from the EFFECT (AUX) bus (4). 10) PHONES plug This plug is for connecting headphones, and outputs the same signal as the MONITOROUT jacks. 11) Level Meter This LED meter displays the level of the signal sent to the MONITOR jacks and the PHONES jack. The 0 segment corresponds to the nominal output level. The PEAK segment lights red when the output reaches the clipping level. 12) STEREO Master Control Adjusts the signal level sent to the STEREO OUT jacks. 6.6 Echo canceller unit Conference systems which include an echo canceller, like Polycom, facilitate easy communication without sound adjustment. However, echo cancellers are not listed as a required item for our activity. This is for the following reasons. Cost We have to buy the device additionally. In case of use with omnidirectional microphones, which are provided Sound Quality with TV conference systems, we have to consider microphone placement for speakers who located far away. There may be some performance problems, like less responsiveness at Performance the beginning of speaking, or bad sound quality. In case of use with omnidirectional microphones which provided with Noise conference system, it s usual to keep unmated status. So these microphones sometime catch background sound accidentally.

9 Basically, the echo canceller is an expensive device and requires a certain level of knowledge and equipment to get high performance. It might be a good option to consider installing if you have a chance to replace teleconference devices. However, if you prepare devices as described above, there should be sufficient performance with certain sound adjustments and microphone handling like switching on and off. The following cases are common matters which cause echo because of uncontrollable sound. Due to DV camera Why couldn t we use the internal microphone of the video camera? Why couldn t we connect a microphone to the video camera? The internal microphone is omnidirectional with auto gain control. So it adjusts sound from the loudspeaker as a very high input, causing echo noise. The auto gain control also works for microphones connected directly and causes echo by high input. Due to microphone Why couldn t we use the microphone which is used for teleconferencing? Microphones which are provided with TV conference systems are omnidirectional and sensitive, so these microphones are supposed to be used with TV conference systems.