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Exchanging Data Files between SIGNAL and MATLAB

Application Note 11 7

2. In SIGNAL, read the floating point (/F) file RFILE into FT buffer 1. The command queries

establish the FT buffer dimensions and time base.

>R FT 1 /B /F

Sample rate: 25000

Time range (msec): 250

No. time steps: 100

Filename: RFILE

Exporting RTS files into MATLAB

The RTS writes and reads only time files. It can write either SIGNAL-header or headerless

files, but can read only SIGNAL-header files. Therefore the RTS can export time signals to

MATLAB as SIGNAL-header time files but cannot import them from MATLAB.

MATLAB Demo Files

SIGNAL provides two MATLAB M-files in \demos which demonstrate some of the above

techniques. TFILE.M demonstrates file import and export commands, and SPECTRO.M

displays two- and three-dimensional spectrograms in MATLAB, based on a spectrogram file

imported from SIGNAL. These demos use three sound files provided in the \sysdata

directory: tweet.1, tweet.f, and tweet.ft. SPECTRO could be the basis for a general

spectrogram display routine. Note: these files were tested with MATLAB version 5.2.

MATLAB Sound Processing Functions

MATLAB version 5.2 offers several sound processing functions, notably the ability to read

and write Wave files (WAVREAD and WAVWRITE) and to play sampled sound data

through the PC speaker (SOUND and SOUNDSC). These functions have the following

limitations.

1. WAVREAD and WAVWRITE handle data only between -1 and +1, truncating any sample

values outside this range. Because SIGNAL's acquisition range is

±10 Volts, these functions

are not recommended for data exchange with SIGNAL.

2. Like all software that plays through the PC's built-in "sound card" hardware, SOUND and

SOUNDSC are restricted to the available hardware sample rates, namely 44100 Hz, 22050

Hz, etc. To accommodate source signals of any sample rate, these functions automatically

resample the playback signal mathematically to the nearest available hardware rate. This will

usually introduce significant distortion, and so these functions are recommended only for

signals with PC-compatible native sample rates.

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Engineering Design NIDisk Betriebsanweisung Seite 31