spdif

[geordie101]

hi,

We have a plan to generate a digital audio signal that represents a 20 kHz analog sinewave, and encode this in SPDIF bi-phase protocol. We would like to generate this from a high speed DI/O card, connect this to the SPDIF IN on a M-Audio Delta 1010LT soundcard, and then use the resulting analog waveform from the soundcard (amplified) to modulate a set of current carrying coils. From my understanding the SPDIF format contains clock information, so that doing it this way allows us to (possibly!?) have a common clock for the audio and for other devices in the system, and avoid any timing problems using the sound VI's in LabView. Has anyone got any suggestions if this is possible, and if anything exists on using a DI/O card to generate digital audio/SPDIF and encode the clock signal?

Cheers,

Mark

[David L.]

Hi Geordie,

Our cards are not pre-configured to output SPDIFF signals. However, there are discrete chips on the market which can take a digital input and clock and create the SPDIFF audio format out.

[geordie101]

Thanks Dave,

From my understanding the SPDIF digital signal is not TTL but some lower voltage, 500 mV or so. So yes, we'll need to have some sort of intermediate conversion stage. My main concern is whether the typical clock speeds on the NI cards (10 MHz), is enough to generate the SPDIF signals, which have a bit rate (at 48kHz sampling) of ~3.2 (I think) MHz? With audio devices there is also word clock, which is just a clock signal to synchronize audio devices and carries no audio data. Has anybody used the DI/O or clock from an NI card in Labview to generate a word clock for audio?

[David L.]

Geordie,

The output rate (10Mhz) will be dependant on what D I/O card you have. I do not know enough about SPDIF to understand why there is a limitation at 48Khz, but will try to help you out the best I can on the National Instruments side of your project.