{"id":2190,"date":"2025-05-31T05:54:19","date_gmt":"2025-05-31T03:54:19","guid":{"rendered":"https:\/\/localdab.org\/?page_id=2190"},"modified":"2025-06-19T07:54:33","modified_gmt":"2025-06-19T05:54:33","slug":"superframe-packing","status":"publish","type":"page","link":"https:\/\/localdab.org\/index.php\/glossary\/q-t\/superframe-packing\/","title":{"rendered":"Superframe Packing"},"content":{"rendered":"\n

(We would like to remind the reader that DAB\/DAB+ uses a sample rate of either 48 kHz<\/strong>, 32 kHz<\/strong>, 24 kHz<\/strong>, or 16 kHz<\/strong>).<\/em><\/p>\n\n\n\n

Superframe packing was a necessary enhancement to adapt the original DAB system for HE-AAC audio coding in DAB+.<\/p>\n\n\n\n

The original DAB standard was designed around audio frames of 24 milliseconds. However, this fixed duration was not compatible with the frame structure of HE-AAC, which required a different frame length. As a result, a new solution was introduced to reconcile these differences.<\/p>\n\n\n\n

For example, we use the most common sample rate in DAB+, which is 48 kHz.<\/p>\n\n\n\n

When transforming audio from the time domain to the frequency domain, it is common practice to use a number of samples that is a power of two. A frame size of 1024 samples<\/strong> would be a logical choice. At a 48 kHz sampling rate, this corresponds to a frame duration of:<\/p>\n\n\n\n

1024 \/ 48,000 = 21.333\u2026 ms<\/strong><\/p>\n\n\n\n

To achieve a cleaner match, we consider reducing the frame size to 960 samples<\/strong>, which results in a duration of:<\/p>\n\n\n\n

960 \/ 48,000 = 20 ms<\/strong><\/p>\n\n\n\n

However, even with this adjustment, we still face a mismatch with the DAB system’s native 24 ms frame duration. The key insight is that the least common multiple<\/strong> of 20 ms and 24 ms is 120 ms<\/strong>.<\/p>\n\n\n\n

This allows for an elegant solution:<\/p>\n\n\n\n