Wodicka G R, Aguirre A, Burns S K, Shannon D C
Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge.
Med Instrum. 1988 Jun;22(3):151-4.
A scheme to reduce the data corruption caused by tape-speed variation in cassette recorders used for monitoring infant apnea was developed. Low-frequency timing information is recorded on the tape, under the constraints of the frequency response of the recorder, simultaneously with the other signals. This information is extracted during playback and multiplied to a frequency suitable for data sampling, using an electronic, phase-locked loop. Analog-to-digital conversion of the data is performed at a rate proportional to the tape speed, resulting in compensation for speed variation. No direct modification of the speed-control mechanism of the recorder is required. The scheme was evaluated by comparing interval measurements of recorded timing information with and without compensation. Compensation reduced the error of the measurement by nearly an order of magnitude, which was consistent with theoretical predictions. This allows analysis of clinical value to be performed on signals recorded by systems that lack sophisticated speed-control mechanisms.
针对用于监测婴儿呼吸暂停的盒式录音机中因磁带速度变化而导致的数据损坏问题，开发了一种方案。在录音机频率响应的限制下，低频定时信息与其他信号同时记录在磁带上。在回放过程中提取该信息，并使用电子锁相环将其乘以适合数据采样的频率。数据的模数转换以与磁带速度成比例的速率进行，从而实现对速度变化的补偿。无需对录音机的速度控制机制进行直接修改。通过比较有补偿和无补偿情况下记录的定时信息的间隔测量值来评估该方案。补偿使测量误差降低了近一个数量级，这与理论预测一致。这使得能够对缺乏精密速度控制机制的系统所记录的信号进行临床价值分析。
