"If it can be written, or thought, it can be filmed..." STANLEY KUBRIC
From Encyclopedia PRO
The DVCAM format is Sony's answer to DVCPRO. The format uses only evaporated metal tape, and has some compatability with DVC. It is not compatible with DVC Pro. In a market that had finally come up with a good standard, all we need is yet another format war! It should be a good one, too as DVCAM looks to be an excellent format.
The DVCAM format has been developed with the robustness and operability required for professional use while maintaining compatibility with the DV format.
In addition to its tape and cassette mechanics, the recorded data also provides full compatibility with DV recordings. This means that full upward/downward tape playback is guaranteed and that signal transfers are accomplished without manipulation to the originally recorded data by use of i.LINK or SDTI (QSDI) interfaces. These features have proven the DVCAM as the most suitable format for integrated use with the widely popular DV transports and DV-based NLE’s.
The DVCAM format also takes into account the requirements in existing linear editing environments. The 15-micron track pitch assures frame accurate and stable editing at the tape edit point. The use of this track pitch also realizes full lip-sync audio and pre-read capabilities.
DVCAM Video Signal Processing
The sampling raster of the DVCAM is the same as that of the ITU-R Rec.601. Luminance video signals are sampled at 13.5 MHz, 720 pixels are transmitted per line for both 525-60 and 625-50 systems.
In the 525-60 system, each color difference signal (CR/CB) is sampled at 3.375 MHz and 180 pixels are transmitted per line (4:1:1). In the 625-50 system, each color difference signal is sampled line sequentially at 6.75MHz, i.e. 360 pixels of either color difference signal is transmitted per line (4:2:0). The decimation filter for the 625-50 system color difference signals is 3 taps FIR filter whose coefficients are 1-2-1 value. The interpolation filter is also a 3 taps FIR filter which has the same value of coefficients as the decimation filter. The sampling start point of CR and CB signals is the same as the luminance signal in both systems.
The sampled video data is reduced by a factor of 5:1 using bit rate reduction, resulting in a transfer rate of 25 Mb/s. Intra-frame coding which adopts DCT (Discreet Cosine Transform) and VLC (Variable Length Coding) is used. To realize a good picture quality at the 25 Mb/s data rate, DV/DVCAM compression adopts a shuffling technique prior to the encoding process. This allows the video to be compressed with maximum efficiency and thus keeps a well-balanced picture quality for any type of images. Note that the data is shuffled only for the purpose of maximizing compression efficiency and thus de-shuffled before recorded to tape.
DVCAM Audio Signal Processing
The audio signal is recorded on two audio blocks. Each audio block is processed independently and identically. The audio block is composed of five audio sectors in five consecutive tracks for the 525-60 system, six audio sectors in six consecutive tracks for the 625-50 system.
Each audio sector is processed in a product block with a dimension of 77 columns by nine rows. Notice that the length of one row in the product block (one sync block) is equivalent to that of video. The same sync block length was selected to simplify the processing circuitry. As with video, audio auxiliary data (AAUX) is multiplexed with each audio sector in the product block. Since audio is sensitive to burst errors, the audio samples are shuffled within the audio block before the error correction data is added in the product block.
Audio encoding modes are defined in each audio block. They are classified by the sampling frequency, bit resolution and the number of channels in the audio block. This standard provides two types of audio encoding modes.
DVCAM technical specifications
The DVCAM/DV formats use metal evaporated tape with a tape width of 6.350 ± 0.005 mm. The DV format specifies two types of tape thickness which are 7.0 μm and 5.3 μm including all tape coatings. The DVCAM format uses only the tape thickness of 7.0 μm to achieve its professional robustness.
Tape width: 6.35 mm Tape speed(s): 28.2 mm/sec Tape thickness: Playing time(s): 40 min (Small); 184 min (Large) Cassette dimensions: 4 15/16 X 3 X 9/16" (Standard DV cass.)
- Track length:
- Track width: 15 um
- Track angle:
- Guard band width:
- Headwheel diameter:
- Speed: 9000 rpm
- Head-to-tape writing speed:
- Head azimuth offset angle (one head):
- No. of segments: No. of lines/segment:
- Control track width:
- Recorded waveform:
- Video modulation or Component luminance channel
- Sync tip frequency:
- Blanking frequency:
- Peak white frequency:
- Color carrier frequency:
- Component color channel
- Chroma encoding:
- Sync tip frequency:
- Center frequency:
- Negative peak frequency:
- Positive peak frequency:
- Digital only
- Data encoding system:
- Data rate:
- Audio segment location:
- No. of longitudnal channels:
- Track width:
- No. of AFM channels:
- Carrier frequencies:
- No. of digital channels: 2 Sampling rate: 48 kHz
- No. of bits: 16 (or, 4 32 kHz, 12 bit channels)