jutta@panix.com
Thu, 12 Apr 2001 10:42:03 -0400 (EDT)
[James P. Salsman]
> If the receiver doesn't understand the audio/wav header, and tries
> to play it as raw GSM, it is short enough, but are there alignment
> issues; which is to ask: If the audio/wav header is prepended to
> the data it encapsulates, can it move the rest of the data out of
> codec frame alignment, distorting the audio decoding?
>
> Jutta: Do you know the answer to that question?
It's possible, but not worth it.
Two problems:
(1) GSM frames themselves come in two incompatible
flavors -- Microsoft WAV and plain (Berlin-toolkit style).
Almost everything with a WAV header is Microsoft-style;
almost everything without is Berlin-style.
Arguably, allowing MS without a header only makes
things worse and more confusing.
(2) The MS GSM frame size is 65 bytes (containing two
bit-packed GSM frames). Unless we add padding
(a padding that wouldn't be added by non-VPIM GSM
recorders), the WAV header will be smaller than
that, and, yes, its presence would throw a reader
out of alignment.
Other than that, having a "noisy" frame in the transmission would
not be a problem; although GSM does build on state established by
previous frames, it recovers quickly from errors.
Personally, I couldn't name a system that understands the MS WAV
format but not the MS WAV header; I don't think this is fixing
a problem that actually exists, while adding a fair amount of
confusion to the spec.
Cheers,
Jutta <jutta@pobox.com>
This archive was generated by hypermail 2.0b3 on Thu Apr 12 2001 - 17:42:15 IDT