Technical Requirements 4.1Categories of Criteria

4Technical Requirements

4.1Categories of Criteria

4.2General Testing Considerations

4.3Test Circuits and Setups

4.3.1General Send Test Setup

Figure 1 – General Test Setup For Send Measurements

4.3.2General receive Test Setup

Figure 2 – General Test Setup For Receive Measurements

4.3.3Send Testing Circuit with Artificial Lines

Figure 3 – Test Circuit For Send Measurements

4.3.4Receive Testing Circuit with Artificial Lines

Figure 4 – Test Circuit For Receive Measurements

4.3.5DC Feed Circuit

• 
  50 Vdc in series with 400 ohms +/- 1%
  
• 
  less than 0.1 dB insertion loss over the 100 Hz to 10 kHz range
  

• 
  At least 30 dB return loss with respect to 900 ohms over the 300 Hz to 10 kHz range
  

1. 
   C >= 100 uF
   
2. 
   L >= 5 H
   
3. 
   R = 200 ohms (including resistance of L)
   
4. 
   V = 50 Vdc
   
5. 
   This is a simplified DC feed circuit. It does not implement the current limit characteristic of modern end offices, which typically limit the maximum current supplied by the office.
   

4.3.6Termination Impedance

4.3.7Source Impedance

4.3.8Artificial Lines

Figure 6 – Artificial Line Segment

Table 1 – Artificial Line Segment Component Values

4.4Transmission Performance

The default test signal for speakerphones shall be the ITU-T Recommendation P.50 male. The long term spectral average of P.50 Artificial Speech is very similar to real speech. Any test signal that produces identical results is considered an acceptable test signal. In the rare case that it can be shown that P.50 is not an appropriate test signal for a specific device, a real speech test signal may be used.

4.4.1Send Performance

4.4.1.1Send Frequency Response

4.4.1.1.1Requirement

4.4.1.1.2Method of Measurement

1. 
   The send frequency response shall beis measured using 0 km, 2.7 km, and 4.6 km artificial lines using the test setup and circuit shown in Figure 1 and Figure 3.
   
2. 
   The nominal P.50 stimulus test signal level shall beis +0 dBPa at the MRP and .
   
3. 
   the test signal for this test shall be the ITU-T Recommendation P.50 male artificial speech signal. Tthe measurement shall isbe made over a minimum range of 100 Hz through 8000 Hz using real-time analysis with 1/3 octave or smaller bands averaged over the entire duration of the test signal. If smaller bands are used then the response shall be band averaged to 1/3 octave before applying the mask.
   
4. 
   The send frequency response is the ratio of the speakerphone electrical output spectrum to the acoustic test stimulus spectrum expressed in terms of dBV/Pa.
   
5. 
   Apply the floating mask limits of Table 2 (shown in Figure 7) to the measured 2.7km frequency response.
   

Figure 7 – Send Frequency Response Limits for 2.7 km

4.4.1.2Send Loudness Rating (SLR)

• 
  A 3 dB increase in the average talking level when using a speakerphone
  
• 
  A 1-2 dB decrease in the actual handset talking levels compared to those measured at the MRP
  
• 
  Other small differences related to different frequency responses, etc.
  

4.4.1.2.1Requirement

Table 3 – Send Loudness Rating (SLR) Limits

1. 
   Loudness rating values represent system losses. More positive values of SLR represent quieter send levels.
   
2. 
   Send Automatic Gain Control (AGC) is a subject for further study which may be addressed in the next revision of this standard.
   
3. 
   The range is +/- 5 dB for the nominal loop. The upper limit is 2 dB louder at 0 km and the lower limit is 2 dB quieter at 4.6 km to allow for the lack of loop compensation.
   

4.4.1.3Send Loudness Rating Directionality (SLRD)

4.4.1.3.1Requirement

Table 4 – Send Loudness Rating Directionality Limits.

1. 
   The intent is to have consistent loudness when the talker is +/- 30 degrees from the center axis.
   
2. 
   The intent is to ensure that there is no more than 3dB gain when the talker is +/- 60 degrees from the center axis.
   

4.4.1.3.2Method of Measurement

1. 
   The Send Loudness Rating is first measured according to 4.4.1.2 at the 0 degree angle.
   
2. 
   The speakerphone is then rotated about its physical center 30 degrees counter-clockwise. Take care to keep the MRP of the artificial mouth at a constant distance from the physical center of the speakerphone, see Figure 8. Repeat the SLR measurement.
   
3. 
   Successively rotate the speakerphone about its physical center to the 60, 300, and 330 degree positions and repeat the SLR measurement at each position.
   
4. 
   Calculate the SLRD for each angle as the difference between the SLR at that angle and the SLR at 0 degrees
   

1. 
   The Speakerphone setup at the 0 Degree position is using the Reference Triangle.
   
2. 
   For the other test positions the Speakerphone is rotated around its the physical center.
   
3. 
   Test table is at least 1 meter square.
   

4.4.1.4Send Distortion and Noise

4.4.1.4.1Requirement

1. 
   The ratio of the signal power to the total distortion and noise power of the signal output shall be above the limits given in Table 5 and Table 6.
   
2. 
   Use IEEE Std 269 to determine if the product is activated for each test point, especially at lower test levels. Activation threshold is dependent on both level and frequency. For any point that is not activated this requirement does not apply. It is recommended that the send distortion and noise performance also be confirmed using subjective listening tests.
   

4.4.1.4.2Method of Measurement

1. 
   Send distortion and noise is measured according to IEEE Std 1329 using the test setup and circuits shown in Figure 1 and Figure 3 with 0 km and 4.6 km artificial lines.
   
2. 
   The test stimulus is white noise band limited to 1/3^rd octave and pulsed 250ms ON, 150ms OFF.
   
3. 
   Apply the test signal at the MRP, at the levels given in Table 6 using the center frequencies and band limits specified below:
   

4. 
   Process the measured data using Hanning Windowing with 5Hz resolution FFT from 100Hz to 6000Hz. After time averaging, remove the data within the notch frequency band specified below:
   

5. 
   Calculate the ratio of the signal power to the total Psophometric-weighted distortion and noise power of the signal output.
   

4.4.1.5Send Off-Hook Noise

4.4.1.5.1Requirement

4.4.1.5.2Method of Measurement

1. 
   The measurements shall beare made in the Off-Hook mode with 0 km, 2.7 km, and 4.6 km artificial lines.
   
2. 
   The speakerphone microphone shall beis isolated from sound input and mechanical disturbances with the. The background noise level shall be less than 29 dBA.
   
3. 
   The measurement shall be taken over a minimum period of 5 seconds.
   
4. 
   Microphone Muting shall is not to be used to provide room noise isolation.
   
5. 
   Per IEEE Std 1329, sSteps should need to be taken to ensure the speakerphone is fully operating in the send mode.
   

4.4.1.6Send On-Hook Noise

4.4.1.6.1Requirement

4.4.1.6.2Method of Measurement

4.4.1.7Send Off-Hook Send Single Frequency Interference

4.4.1.7.1General

4.4.1.7.2Requirement

4.4.1.7.3Method of Measurement

1. 
   The measurements shall beare made in the Off-Hook mode with 0 km, 2.7 km, and 4.6 km artificial lines.
   
2. 
   The speakerphone microphone shall beis isolated from sound input and mechanical disturbances with . Tthe background noise level shall be less than 29 dBA (as specified in IEEE Std 1329).
   
3. 
   Measure the psophometric-weighted noise level with a selective voltmeter or spectrum analyzer with an effective bandwidth of not more than 31 Hz, over the frequency range of 100 to 3500 Hz.
   
4. 
   If FFT analysis is used, then “Flat Top” windowing shall be employed.
   
5. 
   Microphone Muting shall is not be used to provide room noise isolation.
   

4.4.1.8Send Muting

4.4.1.8.1Requirement

4.4.1.8.2Method of Measurement

1. 
   The P.50 stimulus level is 0 dBPa at the MRPSet the Mouth simulator level to 0 dBPa.
   
2. 
   The Send Muting measurement shall beare made with 0 km, 2.7 km and 4.6 km artificial lines.
   
3. 
   This measurement should is be done performed with a narrow band meter that has a noise floor less than –86 dBV.
   

4.4.2Receive Performance

The speakerphone receive volume control shall be set to the applicable Reference Volume Control Setting for the test loop when checking for receive characteristic compliance, unless specifically stated otherwise. The stimulus levels specified for receive tests are specified as 900 ohm nominally loaded (one-half of the open circuit voltage). Following a calibration, the resistive load is removed and the source is connected to the speakerphone without further adjustment.

4.4.2.1Receive Level

4.4.2.1.1Requirement

1. 
   To ensure adequate volume control gain, the CPE shall meet the acoustic level requirements in Table 9.
   
2. 
   To ensure adequate volume control attenuation, the CPE shall have at least one volume control setting that will produce a receive level of less than 60dBSPL with a test level of -18dBV (0km loop).
   

The test signal input levels were derived as follows:

1. 
   High Level (-18dBV): Highest level possible for using P.50 without the PSTN clipping the test signal.
   
2. 
   Nominal Level (-25dBV): Represents the mean Far-End Active Speech Level (ASL) (-28dBm) at the CPE recorded in Bellcore SR-2476 Annex B.
   
3. 
   Low Level (-32dBV): Represents two standard deviations (2 x 4.5dB = 9dB) from the mean Far-End Active Speech Level (ASL) (-37 dBm) at the CPE recorded in Bellcore SR-2476 Annex B. Switched loss (for echo suppression) may squelch lower levels.
   
4. 
   The requirements above would allow acceptable receive levels with average room noise levels. For higher room noise levels and user hearing variability (e.g. hearing loss), a higher output level (i.e. 70 dBSPL) would allow for a better user listening experience.
   

4.4.2.1.2Method of Measurement

1. 
   Configure the CPE and test equipment as shown in Figure 2 and Figure 4.
   
2. 
   The test signal for this test is the ITU-T P.50 male artificial speech signal.
   
3. 
   Set the signal generator for a nominally loaded level per the levels in Table 9:
   
4. 
   The measurement is be made over a minimum range of 100 Hz through 8000 Hz using real-time analysis with 1/3 octave or smaller bands averaged over the entire duration of the test signal.
   
5. 
   The 100 Hz through 8000 Hz measurement result is then power summed and expressed in terms of dBSPL.
   

4.4.2.2Receive Level Directionality (RLD)

4.4.2.2.1Requirement

Table 10 – Receive Level Directionality Limits.

4.4.2.2.2Method of Measurement

1. 
   The Receive Level shall is first be measured according to 4.4.2.1 at the 0 degree angle at -25dBV with a 2.7 km artificial line.
   
2. 
   The speakerphone is then rotated about its physical center 30 degrees counter-clockwise. Take care to keep the grid of the measurement microphone at a constant distance from the physical center of the speakerphone, see Figure 9. Repeat the Receive Level measurement.
   
3. 
   Successively rotate the speakerphone about its physical center to the 60, 300, and 330 degree positions and repeat the Receive Level measurement.
   
4. 
   Calculate the RLD for each angle as the difference between the Receive Level at that angle and the Receive Level at 0 degrees.
   

1. 
   The Speakerphone setup at the 0 Degree position is using the Reference Triangle.
   
2. 
   For the other test positions the Speakerphone is rotated around its the physical center.
   
3. 
   Test table is at least 1 meter square.
   

4.4.2.3Receive Frequency Response

4.4.2.3.1Requirement

Table 11 – Mandatory Receive Frequency Response Limits

Table 11 does not include a mandatory lower limit for frequencies below 400 Hz. It is desirable for the receive response to exceed a lower limit mask value of -7dB for the 315 Hz 1/3 octave band (282 Hz to 356 Hz band edges).

4.4.2.3.2Method of Measurement

1. 
   Configure the CPE and test equipment as shown in Figure 2 and Figure 4.
   
2. 
   The test signal for this test is the ITU-T P.50 male artificial speech signal.
   
3. 
   The receive frequency response shall be measured with the CPE at the Reference Volume Control setting for the 2.7km artificial line using the nominal level (-25dBV) and the test circuit shown in Figure 2 and Figure 4.
   
4. 
   The P50 test signal is applied and the The measurement shall be made over a minimum range of 100 Hz through 8000 Hz using real-time analysis with 1/3 octave or smaller bands averaged over the entire duration of the test signal. If smaller bands are used then the response shall be band averaged to 1/3 octave before applying the mask.
   
5. 
   The receive frequency response is the ratio of the speakerphone acoustic output spectrum to the electrical input test stimulus spectrum expressed in terms of dBPa/V.
   
6. 
   Apply the floating mask limits of Table 11 (shown in Figure 10) to the measured 2.7km frequency response.
   

Figure 10 – Receive Frequency Response Limits for 2.7 km

4.4.2.4Receive Distortion and Noise

4.4.2.4.1Requirement

1. 
   The ratio of the signal power to the total A-weighted distortion and noise power should be greater than or equal to the limits given in Table 12 and Table 13. (AST - Are these really a SHOULD requirement or are these SHALL requirements as with the Send SDNR? If “should” perhaps these requirements can become “shall” after a 2 year period following publication)
   
2. 
   A Receive Level (e.g. -30 dBV) is only to be tested if the measured sound pressure is greater than -50 dBPa (44 dBSPL).
   

4.4.2.4.2Method of Measurement

1. 
   Receive distortion and noise is measured according to IEEE Std 1329 using the test setup and circuits shown in Figure 2 and Figure 4 with 0 km and 4.6 km artificial lines using the applicable Reference VC setting for each loop.
   
2. 
   The test stimulus is white noise band limited to 1/3^rd octave and pulsed 250ms ON, 150ms OFF.
   
3. 
   Apply the test signal at the levels given in Table 13 using the center frequencies and Band Limits specified below:
   

4. 
   Process the measured data using Hanning Windowing with 5Hz resolution FFT from 100Hz to 8000Hz. After time averaging, remove the data within the notch frequency band specified below:
   

5. 
   Calculate the ratio of the signal power to the total A-weighted distortion and noise power of the signal output.
   

4.4.2.5Receive Off-Hook Noise

4.4.2.5.1Requirement

4.4.2.5.2Method of Measurement

1. 
   The measurements shall beare made in the Off-Hook mode with 0 km, 2.7 km, and 4.6 km artificial lines using the applicable Reference VC setting for each loop.
   
2. 
   The measurement microphone shall isbe isolated from sound input and mechanical disturbances with the . The background noise level shall be less than 29 dBA (as specified in IEEE Std 1329).
   
3. 
   The measurement shall be taken over a minimum period of 5 seconds.
   
4. 
   Microphone Muting shall is not to be used to provide room noise isolation.
   
   
   

4.4.2.6Receive Off-Hook Single Frequency Interference

4.4.2.6.1General

4.4.2.6.2Requirement

4.4.2.6.3Method of Measurement

1. 
   Receive noise is measured according to IEEE Std 1329, using the test setup and circuit shown in Figure 2 and Figure 4 except no signal shall be applied at the RETP.
   
2. 
   The A-weighted noise level is measured with a selective voltmeter or spectrum analyzer having an effective bandwidth of not more than 31 Hz, over the frequency range of 100 to 8000 Hz.
   
3. 
   If FFT analysis is used, then “Flat Top” windowing shall beis employed.
   
4. 
   The ambient noise for this measurement shall not exceed 29 dBA.
   
   
   

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