Very simple column-based format using plain text files. The two columns, wave number and amplitude are separated by a semicolon (by default). The wave numbers are stored in descending order.
Has no support for meta-data.
Here is an example:
4000.0;0.36756
3998.0;0.36808
3996.0;0.36847
3994.0;0.36881
3992.0;0.36924
3990.0;0.36968
3988.0;0.37034
3986.0;0.37142
3984.0;0.37234
3982.0;0.37252
3980.0;0.37263
3978.0;0.37322
...