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High Frequency Compression Driver Evaluation
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<blockquote data-quote="Michael John" data-source="post: 51498" data-attributes="member: 830"><p>Re: High Frequency Compression Driver Evaluation</p><p></p><p></p><p></p><p>I'd also be very interested to follow a thread on masking in relation to drivers.</p><p></p><p>Much of my work in the last 14 years has been in audio coder research - MPEG2-AAC, AC3, E-AC3. The coders make significant use of frequency masking our ears to operate and > 10:1 compression ratios. At any given moment in time, the coder calculates a masking threshold as a function frequency, and quantizes the frequency spectrum near that threshold. Any signals lower in level than the mask are thrown away. The bulk of the frequency masking is upwards - i.e. lower frequencies mask upper frequencies. Generally speaking the degree of masking increases with SPL - that is for a given frequency, the masking shape doesn't just rise with the SPL at that frequency, the shape widens. So at higher SPL's, more of the signal will be masked in the ear.</p><p></p><p>More recently coders have pushed compression ratios even high by incorporating spectral replication. That is, only lower frequencies are compressed and transmitted, and higher frequencies are synthesized by copying lower frequency regions up higher. While this may sound extreme, these techniques are backed by a lot of double blind listening tests with expert listeners. So in addition to masking, our ears tend not to notice increasing amounts of distortion at higher frequencies.</p></blockquote><p></p>
[QUOTE="Michael John, post: 51498, member: 830"] Re: High Frequency Compression Driver Evaluation I'd also be very interested to follow a thread on masking in relation to drivers. Much of my work in the last 14 years has been in audio coder research - MPEG2-AAC, AC3, E-AC3. The coders make significant use of frequency masking our ears to operate and > 10:1 compression ratios. At any given moment in time, the coder calculates a masking threshold as a function frequency, and quantizes the frequency spectrum near that threshold. Any signals lower in level than the mask are thrown away. The bulk of the frequency masking is upwards - i.e. lower frequencies mask upper frequencies. Generally speaking the degree of masking increases with SPL - that is for a given frequency, the masking shape doesn't just rise with the SPL at that frequency, the shape widens. So at higher SPL's, more of the signal will be masked in the ear. More recently coders have pushed compression ratios even high by incorporating spectral replication. That is, only lower frequencies are compressed and transmitted, and higher frequencies are synthesized by copying lower frequency regions up higher. While this may sound extreme, these techniques are backed by a lot of double blind listening tests with expert listeners. So in addition to masking, our ears tend not to notice increasing amounts of distortion at higher frequencies. [/QUOTE]
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