the point in time at which the sample begins).ĬD-quality audio uses 16 binary digits to represent the amplitude value of each measurement, or sample. The captured or reconstructed analogue signal is depicted by the red line that runs through the first point of the grey box (ie. PCM-encoded audio.The grey boxes represent samples, amplitude measurements taken at regular intervals of time. So a 44.1kHz sample rate can theoretically store frequencies up to just above 20kHz, approximating the theoretical upper limit of the best human hearing. This is important, because the Nyquist Theorem states that the high-frequency limit of a PCM digital audio system is dictated by the sample rate, and that the sample rate must be at least double the highest frequency that will be recorded. The CD format consists of 44,100 measurements of the waveform's amplitude per second, so is said to have a sample rate or sampling frequency (fs) of 44.1kHz. PCM data consists of snapshots of an audio waveform's amplitude measured at specific and regular intervals of time. The audio is stored digitally on a CD via a technique known as PCM, or Pulse Code Modulation. To put these frequency and amplitude units and specifications in a more modern context, let's define 'CD-quality' audio. By way of example, analogue tape can capture a dynamic range of anywhere between 50 and 70 dB (with 70dB rarely achievable even on the best systems). The dynamic range of an audio system is the range between the quietest sound that it can store or reproduce, or the point at which the quiet sound becomes buried or masked by background system noise, and the loudest sound that can be stored or reproduced before the system becomes overloaded and distorts. not those captured and then played back) can have an incredibly wide dynamic range, and the theoretical dynamic range of human hearing extends from 0dB SPL (Sound Pressure Level) to anywhere between 130 and 140 dB SPL. This applies both to the audio file format and to the recording and playback hardware, though in practice, the lower frequencies are usually more of a problem for the playback system's loudspeakers or headphones than for the format in which the music is stored and disseminated.įrequency response isn't the only important factor, though. Obviously, the lower the lowest frequency that an audio system can reproduce, and the higher the highest frequency an audio system can reproduce, the better. Regarding frequency response, the theoretical range of human hearing is said, broadly, to be 20Hz-20kHz. Let's first identify some key audio concepts and terminology, specifically as they relate to the notion of sound quality. ![]() So what does this compression do to your audio, what are the limitations of these formats, and to what audible artifacts does the data compression give rise? Frequency Response & Dynamic Range All these sources use 'lossy' data-compressed audio formats. The MP3 player, iPod, iTunes and various download formats are now ubiquitous parts of many consumers' listening experience, and let's not forget that many people experience music and other multimedia entertainment via streaming sources such as YouTube, Pandora, Spotify and SoundCloud. ![]() Later generations of converters have sounded much better, making the CD a pretty good format compared to its predecessors. However, it was often criticised for sounding 'brittle' or 'harsh' in the early days - a characteristic that can be blamed on the early generations of analogue-to-digital (A-D) and digital-to-analogue (D-A) converters. When Compact Disc came along, it offered a relatively convenient format with stable and consistent playback speeds, an increased dynamic range, no added format-induced background noise, and no degradation of the storage medium each time it was played. ![]() Listen to some vinyl and cassette and you're going to experience (on one format or the other) limited dynamic range, wow and flutter, clicks and pops, background noise, tonal inconsistencies, and degraded quality, to name a few. ![]() Can you hear the difference between an MP3 and a WAV file? We explain how lossy audio data compression works, and how to spot the tell-tale signs it leaves behind.Īnalogue consumer dissemination formats for audio have all had their problems.
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