diff --git a/src/en/sections/white-noise-adc.tex b/src/en/sections/white-noise-adc.tex index 2c72b22..4057331 100644 --- a/src/en/sections/white-noise-adc.tex +++ b/src/en/sections/white-noise-adc.tex @@ -504,6 +504,91 @@ \subsection{Operation of ADC using temperature measurement as an example} \label{table:adc-temperature-data-example-4} \end{table} +\subsection{Using ADC to record a sound} +\index{Electronics!ADC!Sound recording} + +Sound recording is a good example that we can use to learn some practical +application of ADC. A sound wave receiver is usually a microphone that have a +construction similar to a speaker, but has inverse functionality to it: + +\begin{itemize} +\item In a speaker, changing electric current in a coil creates a magnetic field + that interacts with a permanent magnet which in turn makes a speaker membrane + to vibrate -- and that creates sound waves. +\item In a microphone, sound waves make a membrane vibrate. The membrane is + attached to a permanent magnet, that is enclosed inside a coil. When the + permanent magnet moves inside a coil, it creates the electric current that can + be measured. +\end{itemize} + +Sound recording is a regular measurement of voltage values on the microphone +coil. Each measurement is attached to the timestamp where this measurement was +performed. + +As in the case with the temperature measurement in the section +\ref{subsection:adc-temperature-example}, the quality of sound recording depends +on the frequency of measurements (\emph{sampling rate}) and the ADC resolution. + +Some examples of the standard sampling rates for audio are shown in the table +\ref{table:adc-sound-sampling-rate-1}. Sampling rate directly affects the +maximum frequency of the sound that can be recorded. Theoretically the maximum +frequency that can be recorded is the half of the sampling rate (so called the +Nyquist frequency.) But in reality this limit is slightly lower so the maximum +sound frequency for the sampling rate of 44100Hz is a little bit higher than +20000Hz, but lesser than 22050Hz. \cite{audacityteam:sample-rates} + +\begin{table}[h] + \centering + \begin{tabular}{p{2cm}|p{9cm}} + Sampling rate & Applications \\ + \hline \hline + + 8000 Hz & Old telephone line, walkie-talkie. Not good for the most of the + tasks, but can be useful for some sound effects and to recording the + infra-sound (sound frequencies that are lower than a human ear can hear.) \\ + + \hline + + 11025 Hz & This sampling rate is used to record some low-quality sound. \\ + + \hline + + 22050 Hz & Half of the sampling rate that is used on CDs. Suitable for + digitization of old audio recordings from the 20th century. Also used for + recording human speech where the quality of the sound is not important, but + the clearness of the speech have to be maintained. \\ + + \hline + + 32000 Hz & Suitable for the digitizing of tape recordings and for recording + human speech. \\ + + \hline + + 44100 Hz & The standard quality of audio recordings in CDs. It allows us to + record sound frequencies up to 20KHz, which is considered the limit of human + hearing range for the most people. \\ + + \hline + + 48000 Hz & This standard is used for audio encoding on DVDs. \\ + + \hline + + 96000 Hz & Audio recordings on DVDs and Blu-ray disks. \\ + + \hline + + 192000 Hz & Used on DVDs and Blu-ray disks as well. This quality is often + used in the professional audio recording equipment. \\ + + \hline + + \end{tabular} + \caption{Some standard sampling rates for audio recording.} + \label{table:adc-sound-sampling-rate-1} +\end{table} + %% TODO: Describe 8-bit music in detail here as an example of ADC. \end{document}