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Topic: Conversion, CDQ v. HD to AAC (Read 2164 times) previous topic - next topic
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Conversion, CDQ v. HD to AAC

I generally purchase 24bit HD when it’s available, but 16bit CDQ otherwise. For our car stereo, I will then convert to AAC.

Today I purchased the Cat Power album “Covers” direct from Domino, and it offered downloads in both formats. As a lark, I converted both to AAC with QAAC (- -tvbr 127 -s), and was surprised by the result. The total size of all tracks for the CDQ original was 90Mb, but the conversion from HD was only 75Mb. The results from conversions for all tracks from CDQ resulted in larger bitrates than for having converted HD. Taking 44Hz sampling v 48Hz into account only makes the observation worse.

How does one explain the lower bitrates from HD conversions compared to CDQ from the same source?

Re: Conversion, CDQ v. HD to AAC

Reply #1
It's hard to say without looking at the files, but my guess is that the "HD" version is quieter.

Re: Conversion, CDQ v. HD to AAC

Reply #3
My guess is the 16 bit version was created from the 24 bit version with dither applied, which in itself is good. However, depending on the type of dither used it can add substantial amounts of noise, which is difficult to compress, so you end up with a larger file. You can try for yourself to convert the 24 bit version to 16 bit with the good but rather noisy dither algorithm in foobar and compare the results.
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