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Exchanging Data Files between SIGNAL and MATLAB

Application Note 11 9

Data Precision

Another issue in data storage is different precision levels within each numerical format,

determined by the number of bytes allocated to store each number in the computer.

Obviously, more bytes allow for greater precision and numerical range. Many analysis

systems (including SIGNAL) use data lengths of 2 bytes (16 bits) for integer and 4 bytes (32

bits) for floating point, as described above. However, most computers also provide "double

precision" data types consisting of 4-byte integers and 8-byte floats. These are the default

representations of MATALB, although they are rarely necessary with signals having a

dynamic range of less than 100 db, which includes virtually all acoustic signals. The

following table summarizes the precision and numerical range of these data formats.

Data

Type Precision Range

2-byte integer

±32768

4-byte integer

±2,147,483,648

4-byte float 7 decimal places 10 **

±37

8-byte float 14 decimal places 10 **

±74

Data Byte Format

A final issue in data storage is the order in which the bytes representing a number are stored

in different computer models. This section applies only to users who are running MATLAB

on a non-PC platform, such as Sun or Macintosh, and can be ignored by those who are

running MATLAB on a PC, i.e., the same hardware platform as SIGNAL.

Different computers store the bytes making up an integer or floating point number in

different order in memory. Little-endian format stores the least significant byte first, i.e., at

the lowest memory location, while big-endian format stores the most significant byte first.

Thus the decimal number 1000 = 03e8 hexadecimal would be stored in 16-bit little-endian

format as

8 e 3 0

low address Æ high address

and in big-endian format as

0 3 e 8

low address Æ high address

1 2 ... 28 29 30 31 32 33 34

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