User manual M-AUDIO COW-24

[. . . ] . 20 1 FCC Class B and CE Compliance WARNING: This equipment has been tested and found to comply with the limits for a CLASS B digital device, pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation. This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance with the instructions contained in this manual, may cause harmful interference to radio and television communications. However, there is no guarantee that interference will not occur in a particular installation. [. . . ] A/D Operation The Flying Cow A/D converter accepts analog audio from the left and right Analog In jacks, using either XLR or 1/4" connections. The 1/4" audio input connections accept either balanced (tip-ring-sleeve) or unbalanced (tip-sleeve) signals. The analog signals then pass through the Analog Input Level control and into the A/D converter as balanced signals. Finally, the A/D converter converts the analog data to a digital data stream and outputs it to both the AES/EBU Out and S/PDIF Out jacks simultaneously. IMPORTANT: The same digital data is always present at both the AES/EBU and S/PDIF output jacks. However, the data format of the audio stream will be correct on one jack but not the other (the data format will match the Flying Cow's front panel Digital Format setting). However, if it does, you must set the front panel Digital Format to match the digital output standard you will be using. The A/D converter requires three parameters to be set up for proper operation: Digital Format, Input Level, and Sample Rate. From the front panel controls of the Flying Cow, set the Digital Format to match that of the digital output jack of the external equipment to which you are connecting the Flying Cow (see page 10­Selecting Modes). For example, if you are connecting the Flying Cow S/PDIF Out to the S/PDIF In of a PC digital sound card, set the Digital Format to S/PDIF. For best conversion, the input signal should have enough amplitude to take advantage of all 24 bits of A/D resolution. In other words, the incoming audio signal should be loud enough to approach the A/D converter's maximum acceptable (full-scale) signal level. The Analog Input Level adjustment on the Flying Cow's front panel allows you to attenuate or amplify an incoming signal to properly attain the 11 optimum A/D input level. The Flying Cow front panel A/D Input Level indicators aid in this adjustment. Set the A/D input level knob so that you light as many level indicator LED's as possible without lighting the red Clip LED's. When the Clip LED's light, the audio signal is being "clipped" at the maximum allowable input level of the A/D converter. NOTE: For the absolute best results, set the Analog Input Level to full attenuation ("0" setting) and externally adjust the incoming analog signals to reach the -3 dB levels at peak volume. An occasional CLIP reading is sometimes OK -- it's best to let your ears be the judge!The A/D Sample Rate should be set according to your application's needs (see page 10­Selecting Modes). On the down side, the higher the sample rate, the more digital data has to be stored per second. Quite often, the sample rate you select for the Flying Cow will be dictated by the sample rates accepted by other components in the system such as sound cards, digital audio workstations, CD players, and DAT machines. The Flying Cow supports three standard sample rates: 48 kHz: In the past, this sample rate was reserved for the most costly professional systems. [. . . ] Finally, listen to the Analog Out signals and verify that it matches the known 17 incoming signals with no discernible distortion. Appendix C - Block Diagram LEFT ANALOG INPUT XLR 1/4" ANALOG INPUT LEVEL LED Ladder AES/ EBU S/P DIF Digital Format (changed by Mode Select Switch) Mode Select Switch DIGITAL OUTPUTS AES/EBU RIGHT ANALOG INPUT XLR A/D CONVERTER S/PDIF ANALOG INPUT LEVEL LED Ladder Mode Select Switch 1/4" A/D Sample Rate 48 44. 1 32 Ext (changed by Mode Select Switch) Extracted Clock LEFT ANALOG OUTPUT XLR DIGITAL INPUTS AES/EBU AES/ EBU Mode Select Switch S/PDIF S/P DIF D/A CONVERTER 1/4" Digital Format (changed by Mode Select Switch) RIGHT ANALOG OUTPUT XLR 1/4" 18 Appendix D - Grounding Grounding the shield of a digital cable can sometimes be a tricky issue. In the configuration of audio systems, it is important to avoid ground loops and DC current flowing down the shield of the cable that could result when boxes with different ground potentials are connected. Generally, it is good practice to ground the shield to the chassis of the transmitting unit, and connect the shield through a capacitor to chassis ground at the receiver. This is how the Flying Cow is factory configured and should work fine with most systems. [. . . ]