High sample rate operation, Latency

appendix A • EC-2 96kHz A/D/D/A upgrade

Using the HD24/EC-2 with computer workstations and digital mixers

Because the EC-2 upgrade provides 24 high quality inputs and outputs, it can be used as an external converter to extend the number of analog inputs and outputs of any computer workstations and digital mixers that feature an ADAT Optical interface. When using it as an A/D converter, press the ALL INPUT button with INPUT SELECT set to ANALOG; when using it as a D/A converter, set INPUT SELECT to DIGITAL.

Remember that for an input or output to be active, the current Song must be initialized for the proper number of tracks, even if you’re not recording or playing back the HD24 itself.

For more information see pages 39-40 in chapter 3 of

the HD24 manual, Basic Recording and Playback.

High sample rate operation

If you want to use the HD24/EC-2 with a workstation or digital mixer at the 88.2/96kHz sampling rates, the question to ask the manufacturer of the other unit is: “does this support the ‘sample-split’ implementation for 96kHz audio transmission, with 4 channels of 96K/24-bit audio per ADAT Optical cable ?” The details of this format are outlined by the Alesis Optical Interface Specification Addendum, February 2001. If it doesn’t, instead of treating each lightpipe as a high-speed 4-channel interface, the workstation will use it as the traditional standard- speed ADAT Optical 8-channel interface. If that’s the case, you’ll get apparently “duplicate” signals on the device receiving signal from the HD24 in 96 kHz mode: Track 1 will appear on channels 1 and 2 of the digital mixer or workstation, etc.

In some cases, you need to manually set the other device to send and receive a 96k signal on the ADAT lightpipe. In other cases, you may need to upgrade the software or hardware of the unit so it can interface digitally. Contact the manufacturer of the workstation or mixer for more information.

Latency

Every digital conversion requires a certain amount of time, although the time delay involved is usually less than the time it takes sound to travel one foot through the air. However, if you have a digital workstation that allows compensation for input and output delays, see the Specifications section on page 13 of this manual for latency figures. In most cases, this is only critical when you’re using different interfaces simultaneously (for example, the analog inputs of a computer interface plus its ADAT Optical inputs receiving the output of the HD24). In extremely critical applications, you should test latency matching by using a 20kHz burst tone sent to all inputs simultaneously, viewing the start point of the waveform bursts on the screen of a digital audio workstation, then adjusting the start times of all tracks to compensate.

EC-2 Manual

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