High fidelity

High fidelity [ˌhaɪ̯fɪˈdɛləti:] is a quality standard in audio engineering.

Originally, the guidelines were laid down in the 1960s in DIN 45500. This DIN standard was replaced in 1996 by EN 61305, which only contains procedures for measuring and specifying the performance characteristics, but no longer any minimum requirements, as the once standardized requirements are now no longer seen as a technical challenge.

Engineering

Frequency response

The human ear hears sounds from about 16 Hz to 20 kHz, but the hearing range varies from person to person - an adult has an average hearing range of about 20 Hz to 16 kHz. Humans react most sensitively to sounds between 2 kHz and 5 kHz, so that pitch differences are also best perceived here. For example, DIN 45500 prescribed a linear frequency response in the range from 250 Hz to 6300 Hz for hi-fi home studio equipment, whereby a tolerance of up to 5 dB was permitted. For studio equipment, stricter rules applied according to DIN 45511: Here, only a tolerance of 3 dB was allowed in a frequency range from 80 Hz to 8000 Hz.

Power

The RMS power does not allow any conclusions to be drawn about the achievable volume. While large horn loudspeakers already reach levels of 105 dB with 1 watt, many hi-fi loudspeakers need outputs of up to 200 watts for this level. The power ratings for loudspeaker systems are not standardised. However, the following measured values are required for a reliable statement:

1. (Input) sensitivity or characteristic sound pressure level: This value expresses the volume or sound pressure level produced by the system at 2 volts or 2.83 volts at a distance of one meter (for example: 90dB/2V/1m).
2. "Continuous Power": This value expresses the maximum volume that the system can produce in continuous power. The value is given in dB.
3. Final sound pressure, "maximum power" or "peak value": This value expresses the maximum level that the speaker system can produce before it is destroyed. The value is given in dB.

For a realistic performance specification, the transmission range is required in addition to these measured values. A full-range loudspeaker that has to transmit all audible frequencies (20 Hz - 20 kHz) must produce considerably higher power levels than, for example, a PA high-performance top unit (mid-high loudspeaker approx. 150 Hz - 20 kHz) due to the high loads involved in generating the bass frequencies.

Since the abbreviation Hi-Fi is not protected, compliance with EN 61305 must be checked on a case-by-case basis. Specifications such as music power and especially maximum power or "PMPO" are not exactly defined.

For the so-called RMS power, a power amplifier or loudspeaker must withstand a broadband test signal, consisting of pink noise, of 10 minutes duration without damage and in compliance with EN 61305. This signal is not comparable with music signals (crest factor typically greater than 12 dB) and therefore only allows a statement to be made about the electrical power handling capacity of the loudspeaker, or power amplifier. In most cases, however, especially in the low frequency range, the loudspeaker already reaches its mechanical maximum load below the electrical maximum load, above which the loudspeaker diaphragms can no longer follow the (music) signal. The RMS power therefore only allows limited statements about the maximum level of a loudspeaker. Furthermore, the electrical power handling of a loudspeaker says nothing about its sound quality(s).

In the case of "Dolby surround systems" or "home theatre" or "cinema" systems, the left and right power amplifier/speaker combination (possibly including subwoofer) should meet the hi-fi standard. Weaker guidelines apply to the rear speakers.

Current quality features

At present, EN 61305 no longer plays a quality-determining role in the hi-fi market, since most recording devices, sound carriers and playback devices far exceed these requirements. Only clock radios, simple so-called compact systems in the lower price segment and many car radios as well as all hearing aids still do not guarantee hi-fi-compliant playback today.

Today, a good audio system for music reproduction is expected to have specified data that significantly exceeds hi-fi values. This concerns the frequency transmission range, which should approach the hearing limit of about 20 kHz, but also the distortion factor and the signal-to-noise ratio.

While amplifier technology today is largely mastered in terms of frequency response, noise, signal-to-noise ratio, crosstalk and distortion, the loudspeakers, combined with the room acoustics, continue to be a weak point. Small loudspeakers basically have a problem with the bundled radiation of low-mid frequencies, which is problematic if you want to integrate them into the room acoustics. Loudspeakers have the worst frequency response and by far the highest distortion factor of all components.

In addition, ground loops or hum loops and interference from digital devices can ruin the good signal-to-noise ratios of individual components.