Another AAC encoder currently available is Astrid's Quartex encoder. Decoding for testing was done with the provided Quartex decoder.

Quartex NTT Based 128kb/s Frequency Response

Quartex NTT Based 128kb/s Spectral View

When encoding at 128kb/s Quartex faithfully reproduces the frequency response of the source material up to 17kHz but sharply suppresses everything above 18kHz.

The spectral view shows that all the detail of the source material is present up to 17kHz but that everything above 18kHz is gone. It would seem that this encoder eliminates the shortcomings of NTT's 96kb/s VQF files for all content below 18kHz at the expense of suppressing content above this point.

Listening tests are very favorable of this encoder. On most material I can hear no difference between 128kb/s Quartex encoded files and the original source material. With headphone listening I can not hear any obvious problems with the stereo imaging like I found in the 96kb/s VQF files. Some serious listening on a good pair of speakers will be needed to determine if there is any degradation to the stereo image.

Another pleasant surprise was the low overhead needed to play back the file. CPU utilization was only 25% on my system which is on par with the resources needed to play 256kb/s MP3 files.

There are a couple of problems with the format though. Even though the encoder produces files with an .AAC extension none of the current AAC players can play the file. The only player I have at the moment that can play these files is K-Jofol. Unfortunately encoding is very slow but this is not so important as the codec supports an "idle" switch so you can work on you PC while encoding and only idle CPU cycles will be used for encoding.

In my opinion if this codec was enhanced to allow encoding files at 160kb/s it would be a clear cut winner. As it is I am seriously considering it for all my encoding needs in its current 128kb/s format.

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