Trading (sound engineering)

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In sound engineering, trading is understood to mean the balancing of different perception effects when listening, which is practically applied by applying the Haas effect to the sound system via a PA system in order to keep the audience in the direction of sound of the stage performance .

The human ear uses several different methods to recognize the direction from which a sound event is arriving; compare localization (acoustics) . These perception mechanisms react to different parameters such as volume and interaural time difference . With electronic means it is possible to change such quantities independently of one another. This enables the various mechanisms of directional perception to be “played off” against each other in experiments in such a way that the perceived auditory event remains approximately the same despite changes .

Trading is the opposing action of two quantities and thus the opposite of equivalence .


In the trading attempt, the audio event from the middle of the loudspeaker base between two speakers is deflected in a certain direction by a predetermined fixed transit time difference or level difference and the opposite transit time or level difference is determined which is necessary to bring the audio event back to the "center" , i.e. to compensate for the directional deflection caused by signals in the opposite direction. Trading is the opposite direction "negotiation", so compensating for t Δ - and Δ L - loudspeaker signals . The method is used to learn about hearing sound waves as transit time “intensity” trading in the listening test . Helmut Haas dealt extensively with this psychoacoustic trading effect in Göttingen from 1949 to 1951. One must ask oneself what these tests - also often made with headphones - say when it is determined which transit time difference compensates for a certain level difference or which level difference compensates for a certain transit time difference. The ratio of transit time difference to level difference in μs / dB that can be determined in this way is called the compensation factor or trading ratio; see Haas effect . This means that the louder signal must always appear later; or the quieter signal always earlier.

This compensation factor for loudspeaker signals is approximately Δ t / Δ L = 290 μs / dB.

The compensation factor depends on the volume and the waveform of the signals offered. When compensating the signals, the earlier signal interacts with the quieter signal or the delayed signal interacts with the louder signal in opposite directions (subtractively). The size of the subtractive compensation signals has nothing to do with the size of the signals of equivalence, which act additively in the same direction, i.e. in mixed stereophony. The trading compensation factor Δ t / Δ L is about four times greater than the equivalent factor Δ t / Δ L . This difference between the equivalence curve and the trading curve has not yet been described in the literature. One only seems to know a Δ t / Δ L curve with a large scatter and it is even confusing: "This equivalence is the so-called trading". Avoid Tonverantwortliche trading in their stereo recording, because opposing Δ t - and Δ L - Inter Channel -Signaldifferenzen lead in stereo loudspeaker reproduction with washed, ambiguous auditory events with low localization focus. The important data of the loudspeaker signals in the stereo triangle must be clearly separated from the interaural lateralization signals researched with headphones . The equivalence curve and the trading curve have different origins and do not belong in a representation.

The counterbalancing (compensating) of Δ t - with Δ L signals and vice versa for a central location makes sense in the scientific trading experiments in anechoic room over loudspeakers or in lateralization experiments over headphones, whereby always very fuzzy "fake" Phantom sound sources are located in the middle. The trading effect cannot be used for stereo recordings. There, the equivalence is usefully used to generate the direction.

With the equivalence of stereophony, on the other hand, level and transit time differences are always combined in the same direction. This means that the louder signal must always appear earlier; or the quieter signal always later.

Large deviations between the test results are due to the strong inter-individual fluctuations of the test subjects, as well as the often percussive stimuli that occur in this type of experiment.


  • Headphone lateralization in trading and equivalence: Jörg Damaschke, Michael Granzow, Helmut Riedel, Birger Kollmeier: On the equivalence of interaural time and level differences with short stimuli ( online ; PDF; 1.9 MB).

Web links

Individual evidence

  1. ^ Jens Blauert: Spatial Hearing , Hirzel-Verlag, Stuttgart, 1974, page 132