Recording Characteristics (Subtask 23-70-44-870-006-A01) (1) Memory Characteristics

(a) The SSCVR provides storage for 30 minutes of consecutive recording for each of the four (4) audio input channels, the CMU data, timing data, and ancillary data (memory pointers, elapsed time, etc.) into CSMU memory. A 2-hour duration recorder is also specified as an option. The CSMU memory has a maximum bit error rate of 1 in 100,000 bits and a

minimum rewrite capability of 100,000 cycles. Each separate physical memory device in the CSMU memory includes an electrically embedded identification to ensure proper sequencing of the data in the unlikely event that the memory devices become dislodged from their correct positions on the circuit board (possible following a severe accident).

(b) Recording of data to the solid state memory array is partitioned such that the narrow band voice channels are stored in physically separate devices from the wide band area channel. This provides data redundancy in the unlikely case of memory device failure.

Digital communication, timing, and rotor speed data is embedded within the audio data as it is received.

(2) Timing Characteristics

(a) Upon the application of electrical power, the SSCVR begins storing digital audio data to the crash survivable memory within 250 milliseconds. The delay in recording of the digital audio information from the time of reception at the SSCVR input to the time of recording in the CSMU memory does not exceed 50 milliseconds. The recorded digital audio data on each of the four channels is synchronized in time to within five milliseconds. The time correlation of the arrival time at the SSCVR of the CMU message is within five seconds.

(b) When the memory bulk erase discrete is activated for a duration of longer than 1/2 second, the SSCVR initiates a bulk erase function. The erase function is completed within five seconds of activation.

(c) When the test input discrete is activated for a duration of longer than 1/2 second, the SSCVR provides self-test status results in both an aural and visual means within three seconds upon successful completion of self-test. In the case of a failed self-test, no indication is given at the microphone monitor; however, the maintenance discrete will be set to the failure mode.

(3) Audio Performance

(a) The SSCVR provides audio recording and playback performance as summarized in Table 3.

Table 3. Audio Performance Summary

Channel

(MIN) SNR (MIN) STI (MIN) Balance

S/N Signal

1 500 mVrms 150 to 6,000

Hz

25 dB 0.85 ±3 dB 48 dB 40 dB

10,000 ohms Wide band

1 Number of Channels

a The SSCVR is capable of simultaneously recording three narrow band voice and one wide band area audio channel.

2 Input Level and Impedance

a The SSCVR audio input impedance for each channel is 9,000 to 11,000 ohms.

The SSCVR is designed for an input signal level of 10 mVrms minimum and 500 mVrms maximum (2.5 Vrms on narrow band channels and input dynamic range of 34 dB). Each of the four audio input channels include a two terminal input isolation circuit to isolate the input from analog ground and the supply voltages. The audio input channels also include transient and EMC protection.

3 Balance Between Channels

a The SSCVR audio recording channels are balanced such that the audio signals produced during playback do not differ by more than a total range of 6 dB.

4 Audio Frequency Response

a The frequency bandwidth of the three narrow band voice channels is at least 150 to 3500 Hz with a pass band characteristic of ±3 dB. The frequency bandwidth wide band area channel is at least 500 to 6000 Hz with a pass band characteristics of ±3 dB.

5 STI

a STI is an objective measure of speech transmission quality which can be related to subjective quality tests. The STI factor is a number from 0.00 to 1.00. An STI above 0.75 is considered excellent quality. The STI measurement provides another measure of audio recording quality beyond historical SNR measurements.

b The reproduced audio signal for the wide band area channel has a minimum STI rating of 0.85 and the three wide band voice channels have a minimum STI rating of 0.75.

6 S/N + Distortion Ratio (S/N + D)

a The minimum S/N plus distortion ratio (S/N + D) for all four channels is 24 dB for the full duration of the recording and for input signal amplitudes between 0 dB and 20 dB of the maximum input amplitude. This S/N + D is achieved for the full bandwidth of each channel.

7 Audio Noise Level (No Input Signal)

a With an open or short circuit condition on the input, the level of the noise recorded in the crash survivable memory is at least 48 dB below a recorded signal in the crash survivable memory with an input signal at the frequency of the maximum response of the channel and maximum input amplitude.

8 Crosstalk Between Channels

a The crosstalk between audio channels does not exceed 40 dB for both audio and data signals.

9 Audio Monitor Channel

a The SSCVR provides an audio monitor output channel which is the composite of the four audio input channels. A secondary function of this output is to provide an aural test tone to indicate successful completion of initiated self-test. The audio monitor channel has an output impedance compatible with a standard 600 ohm headset.

(4) CMU Recording Characteristics

(a) The SSCVR receives and records CMU information at the CMU ARINC-429 input as data becomes available. The interface complies with ARINC-429 for a low speed bit rate. The data rate for this input channel must not exceed 3 messages each minute, 128 characters each message. The message is recorded in solid-state memory within 5 seconds of receipt at the channel input.

(5) Time Recording Characteristics

(a) The SSCVR receives and records timing data from either the Captain’s clock through ARINC-429 low speed channel or from a FDAU or FDR through an FSK modulated ARINC-717 like signal. The SSCVR records timing data every 4 seconds at an ARINC-717 frame rate.

(6) OMS Characteristics

(a) The SSCVR provides BITE information (status) to an OMS through a low speed ARINC-429 interface. The SSCVR contains the hardware to perform this function but does not initially include the software functionality to provide this interface.

H. Design Characteristics (Subtask 23-70-44-870-007-A01)