Digital Audio - Characteristics of a sound card

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In this section we will take a look at the technical details that characterize an audio card:

  • Inputs: the card's inputs can be either analogue or digital. In the first case signals pass through the sampling stage and get converted into digital, whereas in the digital domain they are sent directly to the DSP card. Various connectors are used: RCA, TRS, XLR (for analogue signals) and AES/EBU, S/PDIF (for digital signals). [Connections, wires and connectors ]

  • Outputs: the analogue outputs that are available are usually wired on RCA connectors. The digital outputs are of the following kind: AES/EBU, S/PDIF [Sync mode ] .

  • Full-duplex: professional HD systems require this function which allows us to listen to tracks that have been recorded previously and simultaneously record new tracks. It is the equivalent of the sync mode in analogue recorders. [Functioning modes ]

  • Noisiness of the AD-DA converters: the sampling process introduces noise which is mainly caused by the circuitry. This is why it is very important that the sampling circuit is external to the computer and not set up inside it, where it would be exposed to numerous electromagnetic interferences.

  • Sampling frequency and quantization bits: in commercial CDs the sampling frequency that is used is 44.1 KHz with a 16 bit quantization. With HDR systems it is advisable to have better performances, because all the manipulations that have taken place so far, starting from the input signal down to the output return of the signal, introduce a degradation. This occurs because the mathematical calculations that are carried out by the system take place on digital data and therefore every calculation introduces an approximation. That's why it is best to work with higher performances, for example, to sample at 96 KHz with 24 bit, then carry out all relevant manipulations, and only at the end reconvert it all to our usual 16 bit/44.1 KHz.

  • MIDI, MTC, SMPTE plugs: as already mentioned, these plugs allow the HDR system to communicate with other audio sytems in synchrony. [SMPTE time code ] [MTC - MIDI Time Code ] [The Midi Protocol ]


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