Although the digital recording technology used in CDs is inherently better than a tape cassette's vintage analog tech, the sound quality for the best cassettes used in the best tape decks isn't far behind. Because sound quality can be highly subjective, technical specifications are helpful when you're comparing different recording media.
Dynamic range is the ratio between the loudest and quietest sounds possible on a recording medium, and is expressed in decibels. The bigger the number, the better the dynamic range. This number is important as it gauges how well a medium preserves loudness levels in music; a smaller dynamic range gives music a "cramped" sound. A typical dynamic range figure for a good-quality cassette is about 50 dB; however, cassette decks equipped with Dolby or DBX noise-reduction circuits can push the figure to 75 dB. Compact discs have dynamic rage of 96 dB.
A medium's frequency response is a measure of how faithfully it reproduces bass, midrange and high frequencies. The CD itself has a frequency response of 2 Hz to 21 KHz, although individual players may have filters that limit the extreme low and high frequencies slightly. Cassette frequency response varies a great deal and depends on the kind of tape and player. Some of the best tape decks, using chromium dioxide tapes, have a range of 20 Hz to 20 KHz.
Signal-to-noise ratio is a measure of the degree to which noise intrudes on your recordings, whether you can hear noise in the music or whether noise is inaudible even in moments of silence. As with dynamic range, SNR is expressed in dB. Cassette are inherently noisier than CDs due to the nature of magnetic tape; however, noise reduction can greatly improve SNR. The SNR of CDs is about the same as the dynamic range -- 96 dB. The SNR of a good-quality cassette deck can range as high as 80 dB with noise reduction.