Engineering Design NIDisk Betriebsanweisung PDF herunterladen (Seite 12)

NIDisk User Guide

Sample rate may be selected from the drop list of available sample rates in Hz or entered

manually. Available sample rates vary with the specific I/O card. They are a subset of the

submultiples of some fixed frequency, such as 20 MHz for the PCI-6251. Due to this

mathematics, the drop list typically displays all available high frequency rates and a subset of

the low frequency choices, which are very dense.

Gain sets the gain applied to the input signal before digitizing. Gain is specified as a

multiplier (rather than dB). Available gains vary with different I/O cards.

No. channels can be set to any nymber between 1 and 8. Input sample rate is usually limited

to the maximum sample rate of the I/O card divided by the number of channels. Thus a

500 kHz card can sample two channels at 250 kHz per channel.

Filename specifies the destination sound file. If the filename does not include a full path

(drive letter and directory), files are stored in the directory containing NIDisk. Embedded

spaces are allowed in the filename. NIDisk will append the ".wav" extension to Wave files if

not included.

For a one-channel acquisition, Filename simply specifies the name of the destination sound

file.

For a multi-channel acquisition, the Filename specification depends on the Channel format

setting. With "One file per channel" (the recommended setting), specify the File prefix and

NIDisk will store the data, one file per channel, in SIGNAL files prefix.1, prefix.2, etc. or

Wave files prefix.1.wav, prefix.2.wav, etc. File prefixes should not end with a period (.).

With "Multi-channel file", specify the Filename and NIDisk will store all acquisition

channels in this file (see Channel format). Note that multi-channel SIGNAL files require

SIGNAL 4.1, and Wave files with more than 2 channels may require special software.

File type may be SIGNAL or Wave. Sound data are written as 16-bit integers, coded as

follows. SIGNAL files are strongly recommended.

• SIGNAL files are written in the native 12-bit or 16-bit coding of the installed I/O

board, with offset removed from 16-bit data. A conversion factor is stored in the file

header that allows SIGNAL to reconstruct the original voltage range.

• Wave files are written in 16-bit coding (0 offset, ±32768 range), independent of the

installed I/O card. Offset is removed and 12-bit data are scaled to 16 bits. Files are

uncompressed, i.e., in the "PCM" or "type 1" standard

Wave file format.

• Note that Wave file amplitudes may not scale correctly in SIGNAL, since the

Wave header contains no conversion factor to indicate the original voltage range

of the data.

• Note also that Wave files with sample rates other than 44,100 Hz may not be

playable on all systems.

Channel format indicates how to store multi-channel acquisition data. One channel per file

stores each acquisition channel in a different file (see Filename). Multi-channel file stores

all channels in one file, interleaved, e.g., point 1 of channel 1, point 1 of channel 2, point 2 of

channel 1, point 2 of channel 2, etc. for a 2-channel acquisition.

Overwrite allows NIDisk to overwrite pre-existing data files of the same name without

warning the user. If Overwrite is not checked, NIDisk will request permission before

overwriting.

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