A few years ago, the BBC performed a series of listening tests to determine whether it would be of significant benefit to their listeners to transmit lossless (FLAC) recordings.
A 320 kbps AAC recording was played from a high quality decoder and a triple blind test performed over several days
The results determined that a 320k AAC (lossy recording) was statistically indistinguishable from the original. Obviously high quality equipment was used, but what this was, was not revealed
The document is 14 pages long
The summary at the end states:
This paper presented a subjective listening test to determine whether there is likely to be a perceptible difference between lossless (FLAC) and AAC 320 kbps compression.
Recommendation
ITU-R BS.1116-3 was used as guideline for the design process. A total of 18 participants took part in the test and each graded 12 test items on the ITU 5-grade impairment scale. The results
were analysed using difference grades with statistical methods, such as t-test and ANOVA. The post-screening process was used to eliminate the scores of 5 participants.
The analysis showed that there was no statistically significant difference in quality between the uncompressed signals and AAC-LC 320 kbps compression, which means participants did not perceive
difference between two formats. It also showed that there was a statistically significant difference between the uncompressed signals and HE-AAC 48 kbps compression. This means participants
could perceive differences in quality between the two formats.
The test has shown how AAC encoders can preserve the quality of the original audio. This suggests that offering lossless audio might not have a great benefit in terms of quality increase to the
consumers. However to ensure that a delivery service is transparent and original quality is always maintained, a lossless codec would be required.
https://downloads.bbc.co.uk/rd/pubs/whp/whp-pdf-files/WHP384.pdf
A 320 kbps AAC recording was played from a high quality decoder and a triple blind test performed over several days
The results determined that a 320k AAC (lossy recording) was statistically indistinguishable from the original. Obviously high quality equipment was used, but what this was, was not revealed
The document is 14 pages long
The summary at the end states:
This paper presented a subjective listening test to determine whether there is likely to be a perceptible difference between lossless (FLAC) and AAC 320 kbps compression.
Recommendation
ITU-R BS.1116-3 was used as guideline for the design process. A total of 18 participants took part in the test and each graded 12 test items on the ITU 5-grade impairment scale. The results
were analysed using difference grades with statistical methods, such as t-test and ANOVA. The post-screening process was used to eliminate the scores of 5 participants.
The analysis showed that there was no statistically significant difference in quality between the uncompressed signals and AAC-LC 320 kbps compression, which means participants did not perceive
difference between two formats. It also showed that there was a statistically significant difference between the uncompressed signals and HE-AAC 48 kbps compression. This means participants
could perceive differences in quality between the two formats.
The test has shown how AAC encoders can preserve the quality of the original audio. This suggests that offering lossless audio might not have a great benefit in terms of quality increase to the
consumers. However to ensure that a delivery service is transparent and original quality is always maintained, a lossless codec would be required.
https://downloads.bbc.co.uk/rd/pubs/whp/whp-pdf-files/WHP384.pdf
