An encoder for mixing - a plurality of mono audio channels into - a stereo audio signal recording comprising mixed samples for storage in an audio track of a storage device and - each mono audio channel comprising a first number of samples per unit time, - each mono audio channel having the same number of samples per unit time, and same time reference, - the audio signal comprising less mixed samples per unit time than a sum of the number of samples per time unit of all mono audio channels used in the audio signal, and characterised by the encoder being adapted for: - attenuating at least one mono audio channel using at least one attenuation coefficient, - deriving approximated samples by interpolation filtering samples of the respective mono audio channels, - approximated samples being intermediate in time with respect to original samples, the original samples of each one of the plurality of mono audio channels forming a regular pattern staggered in time with relation to every original sample of every other one of the plurality of mono audio channels, - summing a first original sample of a first one of the plurality of mono audio channels and a first approximated sample derived from a second one of the plurality of mono audio channels to obtain a first mixed sample, and for summing a second original sample of the second one of the plurality of mono audio channels and a second approximated sample derived from the first one of the plurality of mono audio channels to obtain a second mixed sample, each of the second samples having timings which are successive to timings of each of the first samples, the encoder further being adapted for: - generating a set of additional parameters for mastering the audio track of the storage device comprising the audio signal recording, - the set of parameters comprising interpolation filter parameters, attenuation coefficients and samples allowing a calculation of the first sample of the first one of a plurality of mono audio channels and the second sample of the second one of a plurality of mono audio channels from the first mixed sample. - a plurality of mono audio channels into - a stereo audio signal recording comprising mixed samples for storage in an audio track of a storage device and - each mono audio channel comprising a first number of samples per unit time, - each mono audio channel having the same number of samples per unit time, and same time reference, - the audio signal comprising less mixed samples per unit time than a sum of the number of samples per time unit of all mono audio channels used in the audio signal, and characterised by - attenuating at least one mono audio channel using at least one attenuation coefficient, - deriving approximated samples by interpolation filtering samples of the respective mono audio channels, - approximated samples being intermediate in time with respect to original samples, the original samples of each one of the plurality of mono audio channels forming a regular pattern staggered in time with relation to every original sample of every other one of the plurality of mono audio channels, - summing a first original sample of a first one of the plurality of mono audio channels and a first approximated sample derived from a second one of the plurality of mono audio channels to obtain a first mixed sample, and for summing a second original sample of the second one of the plurality of mono audio channels and a second approximated sample derived from the first one of the plurality of mono audio channels to obtain a second mixed sample, each of the second samples having timings which are successive to timings of each of the first samples, the encoder further being adapted for: - generating a set of additional parameters for mastering the audio track of the storage device comprising the audio signal recording, - the set of parameters comprising interpolation filter parameters, attenuation coefficients and samples allowing a calculation of the first sample of the first one of a plurality of mono audio channels and the second sample of the second one of a plurality of mono audio channels from the first mixed sample.