Chapter 4. From Digital Audio to Analog Sound
4.1. Digital to Analog Converter
Here we are. Our trip comes to an end. The recorded sound travelled first through a microphone membrane to generate electrical impulses, then through various cables and electronic components, into a converter to transform the analog signal into a digital signal so that the power of computers can be used to work on the sound; the signal must then pass through another converter (see below) before being transformed into moving air molecules by another transducer like a speaker (section 4.2) to finish its journey in our ears (section 4.4). We will make a short journey through acoustics to understand why that is important when we listen to sounds in a physical space like a room (section 4.3).
Digitized information is now ready to be sent from the DAW to a Digital to Analog (DA) converter – this is the DA converter role depicted in Figure 5. DA converters can be found in PC sound cards, MP3 players, audio interfaces and standalone devices.
Simply because our ears cannot hear digital information too well. Our ears need air molecules pushing against our internal eardrum. That is in the analog domain, so we need to send our digital information through a DA converter.
Remember the Nyquist-Shannon theorem from section 3.1? We know that we can reconstruct a signal with the same quality as the original signal. A typical DA converter works like this: it transforms the discrete step-like digital (virtual) signal into a discrete step-like physical signal by producing an electrical impulse each time a bit of data passes through; the voltage of that electrical impulse is kept constant until the next bit of data passes through. Interpolation techniques allow this constant voltage to be changed into more continuous signals by having the DA converter guess what the original voltage might have been. A low-pass reconstruction filter is used to weed out frequency artifacts. DA converters possess the same characteristics as their AD cousins: bit-depth, sampling rate, dynamic range; they are subjected to the same problems as well (jitter, noise, etc.).
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