Now to zero crossings and splitting on block boundaries. Sit back - this is not a ten-word issue. And in all this, remember that what you are hearing is a bitstream, not distinct tracks. One more caveat: I know Sound Forge and many other WAV editors only by reputation. The ones I use regularly are GoldWave and CoolEdit Pro.
A track is a collection of sequential blocks of that bitstream and is designated in the TOC. Tracks must be split on block boundaries. Addressing in the TOC is in terms of blocks and you cannot split more finely than that. Each block on an audio CD is 1/75th second. For SMPTE, it's 1/30th, for other purposes, it's other sizes, but we're talking CD-DA, so it's 1/75th.
If the split occurs on a block boundary and if you burn DAO, then the sound is continuous across the split and there is no click or silence or other artifact - the bitstream is continuous and the sound is uninterrupted. If your split is not on the block boundary, then the block has to be filled with something.
By splitting at a zero crossing, the program presumably fills the rest of the block with zeroes for you. That's fine - if you want a silence which may be as long as (almost) 1/75 second. Sound Forge is right that you won't get a click, but you will get a momentary dropout, sort of an inverted click, if the zero crossing did not occur during an extended silence. The advantage of splitting at a zero crossing is not for writing to CD-R but for listening to the WAV. If you pick a high-amplitude signal to end a block (on the screen), then play it, you will hear a distinct noise at the end. The signal has dropped abruptly to zero. If you do the same thing at a zero crossing, you do not hear the click. Again, this is for listening to the WAV directly, not for recording in CD-DA where the block must be filled.
If you use a program which does not split on a block boundary, *something* must be used for the missing bytes and now there is no supply of zeroes for the job. I am told (I haven't verified it) that the program may pick up whatever debris is around from the stream of data from your source. It might even be the next few milliseconds of the audio - but in that case, they will be repeated. At best, it might fill with zeroes (see the issue above), but regardless you will not have continuous sound across the split. So the way to get a clean split for continuous play is to split the track at the block boundary. CDWAV and GoldWave force you to do that. In allowing for alternate frame rates, CoolEdit gives you the option to vary it. My understanding is that Sound Forge provides the option as well. And zero crossing has nothing to do with block (frame) boundaries.
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