mp3PRO Compatibility
The most important fact about mp3PRO is that mp3PRO is completely backwards and
forwards compatible with mp3. That means:
An mp3PRO decoder is able to decode all mp3 and mp3PRO
encoded content.
An mp3 decoder is able to decode mp3 and mp3PRO encoded
content
(however, mp3PRO files are decoded without the dramatic mp3PRO
improvements).
An mp3 encoder is (obviously) only able to create mp3
encoded content.
An mp3PRO encoder is able to create mp3PRO encoded content
and mp3 encoded content.
mp3PRO and mp3 in one single product?
Due to the above, there is absolutely no need to include an mp3 decoder and an
mp3PRO decoder in one single product, since the mp3PRO decoder is able to
decode all mp3 and mp3PRO encoded content.
There is also no need to include an mp3 encoder and an mp3PRO encoder in one
single product, since the mp3PRO encoder is able to produce mp3 and mp3PRO
encoded content.
Summarizing, there is no need to include both (mp3 and mp3PRO) in one single
product.
How will mp3PRO content play on mp3 players?
The mp3PRO technology is a dual-rate system. The backwards compatible mp3 audio
bit stream is run at half the sampling rate than the enhancement, thus to be
able to generate mp3PRO bit streams the digital audio input data must be
sampled at 32 kHz or above (44.1 or 48 kHz recommended).
That means:
mp3PRO content played on an mp3PRO decoder will have sampling
frequencies of 32 kHz, 44.1 kHz or 48 kHz.
The same mp3PRO content played on an mp3 decoder will result in sampling
frequencies of 16 kHz, 22.05 kHz or 24 kHz.
The number of channels will not change whether such mp3PRO content is played on
an mp3PRO system or on an mp3 system, in case of "mono" and "stereo" content.
In addition to the "mono" and "stereo" formats, the mp3PRO format
adds the so called Low-Complexity Stereo ("LC Stereo") technique
to the plain mp3 format:
Mono mp3 content can be enhanced not only by applying the usual PRO enhancement
for higher audio bandwidth, creating monoaural mp3PRO content, but also by LC
stereo to make it a stereo channel mp3PRO bit stream.
This feature is designed to allow stereo coding even at extremely low bit
rates. A plain mp3 decoder however would play LC stereo enhanced mp3PRO
bit streams as mono.
That means (for LC stereo encoded mp3PRO content):
LC stereo encoded mp3PRO content will play as "stereo" on an mp3PRO system
(at sampling frequencies of 32 kHz, 44.1 kHz or 48 kHz).
The same LC stereo encoded mp3PRO content will play as "mono" on an mp3 system
(at sampling frequencies of 16 kHz, 22.05 kHz or 24 kHz).
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