June 2, 2021

Analog vs Digital Audio Explained

The debate between analog vs digital audio has been a divisive one since the early development of digital audio in the 1960’s. Rather than try to fight for one side or the other, the aim of this article is to compartmentalize the two formats in order to allow you to understand how both realms are commonly integrated with today’s recording practices.

To comprehend analog vs digital sound, we’ll have to begin by understanding that sound itself is a continuous wave of audible pressure that can transmit through various forms of matter; liquids, solids and gases. The sound waves that are produced by a source, whether it be a human vocal, an acoustic guitar’s resonating strings, or the hammering of a piano, are all considered analog signals because of their time-varying quantity. In order to capture this continuous wave, an analog recording system is required in order to assure that the signal received by the microphone is an exact representation of what’s written onto a tape recorder or vinyl disk. For this reason, analog is believed to be an ideal representation of the sound at the moment it was recorded.

Digital sound differs in the sense that digital audio refers to the implementation of binary code, a digital language of ones and zeros, that seek to recreate an analog waveform by representing a sound wave’s pitch and intensity at a variety of intervals. In order to capture a vocal performance, a microphone will capture an analog signal that will then be converted to a digital waveform with the use of an analog-to-digital converter (ADC). This ADC will recreate the waveform using binary code and then the digital signal will go through a digital-to-analog converter (DAC) in order to be played back. Having gone through the various stages of conversion, compression followed by expansion leads to the sound wave’s quality being altered. When recording audio into a digital audio workstation (DAW), such as ProTools, it’s necessary to understand that the conversion taking place between recording and playback will play a significant role in how the output signal is reconstructed. An imperative takeaway from this process is that all signals begin as analog and only become digital upon conversion to that format. With the advancement of digital technology, binary code has become an extremely accurate reproduction of analog signals in their purest form.

To better simplify analog vs digital audio, analog is to “capturing” what digital is to “reconstructing”. Whereas analog sound is captured as a single waveform, digital formats recreate the original analog signal as a composite of numerous segments using binary code. These segments are meant to represent various moments pertaining to different intensities and pitch. Because of the infinite possibilities presented by analog signals that digital signals can’t reproduce perfectly, digital sound commonly misses bits of the sound waves due to the quantization error. The quantization error is the difference between the actual analog value and the approximated digital value due to the rounding that occurs during conversion. Quantization error also introduces quantization noise to the sample as a byproduct of the misrepresented conversion. The higher the resolution of the ADC, the lower the quantization error will be, hence a lower noise floor. As digital recordings improve, the misrepresentations between the actual analog signal and the digital approximation will continue to diminish. Below is a representation of what the generated wave (digital signal) will look like in relation to the precise wave (actual analog signal) with the green, saw-shaped waveforms representing the quantization error.

Analog vs digital audio, visualized.

If you’re interested in learning about more audio techniques, consider F.I.R.S.T. Institute’s Recording Arts & Show Production program, which teaches students audio fundamentals in just 11 months.