Uncompressed audio - don't record to extend p2?

R

RogerandOut

Active member
If you don't record any audio data with the HVX will there be more space to record images?

I think I would rather record the audio with a portable field recorder.
 
alpi69 said:
a very good idea. don´t know how much space you save, but it might bew more than we think.
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Thanks. I am wondering about the difference in sound quality between recording in 16 bit and 24 bit. So then I started wondering how much storage space would be saved by not recording any of the audio by the HVX.

I guess it depends upon how much space is consumed by uncompressed 16 bit audio, which as you say could be significant.
 
The audio overhead is pretty minimal, as compared to the video. The HVX records four tracks of 48khz uncompressed audio, I think the total space requirement is just 3 megabits per second for all four tracks.
 
Makes me wonder why HDV in 720P dont use the full bandwith for uncompressed audio. Whats really the reason they stayed at 19 mbs?
 
JVC's flavor of HDV is 19 megabits, and I believe the justification for that is that it matches the ATSC broadcast transmission standard.

Sony's flavor of HDV is 25 megabits, mainly because that's the maximum they could get on a DV tape.
 
MovieSwede said:
Makes me wonder why HDV in 720P dont use the full bandwith for uncompressed audio. Whats really the reason they stayed at 19 mbs?
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Actually, let's revisit this question: apparently JVC *does* use the full bandwidth for uncompressed audio as well. Apparently, while it records 384kbps of audio into the HDV MPEG-2 data stream, it also simultaneously writes out uncompressed PCM audio in the unused audio section of the DV tape. So if you tell the camera to read the tape as if it's HDV, it'll read the video and compressed audio. If you then rewind and re-capture, but this time tell the cam to read the tape as if it's DV, it'll read the raw PCM audio off the DV audio track portion of the tape. It would mean a two-pass capture process, but hey -- it's better than not having it there at all!

Steve Mullen tried it and was unsuccessful in getting consistent performance, he got one channel one time, and then later couldn't get any PCM. I found a menu item that seemed like it would help, but I've already sent the HD100 back so I can't do further testing. Maybe Nate or Tim could do some testing and figure out the procedure.
 
Barry_Green said:
The audio overhead is pretty minimal, as compared to the video. The HVX records four tracks of 48khz uncompressed audio, I think the total space requirement is just 3 megabits per second for all four tracks.
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so does that audio info account for about 10 percent of the total when video and audio are recorded together?
 
If you're recording 1080, audio accounts for about 3% of the data rate. If you're recording 720/24p, audio would account for about 7%.
 
Barry_Green said:
The audio overhead is pretty minimal, as compared to the video. The HVX records four tracks of 48khz uncompressed audio, I think the total space requirement is just 3 megabits per second for all four tracks.
Click to expand...

Your correct, almost to the byte! 16 bit PCM is 2 bytes per sample (COB format) so four channels is 8 bytes per sample. Multiply this by the sample rate (48 kS/s) and you get 384,000 Bytes/s or 3072000 bits/s.

Not much overhead when compared to either 100 or 50 Mb/s. If I am understanding the format correctly, even if no audio is assigned, the space is allocated (intervealed) in the data stream.
 
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