I have found the iMac output specifications for the optical output:
During playback of a 1KHz, full-scale sine wave (S/PDIF output format, 44.1KHz output sample rate, 24-bit sample depth, unless otherwise specified) the digital audio output has the following nominal specifications:
Jack Type: 3.5mm Optical Jack
Output Data Formats: S/PDIF (IEC60958-3), AC3
Output Sample Rates: 32KHz, 44.1KHz, 48KHz, 64KHz, 88.2KHz, 96KHz
Bits per Sample: 16 or 24 (S/PDIF),16 (AC3)
Frequency Response: 20Hz – 20KHz, +/-0dB
Signal-to-Noise Ratio (SNR): >130dB
Total Harmonic Distortion + Noise (THD+N): <-130dB (0.00003%)
Channel Separation: >130dB
Good specs.
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