bdf_ChanOps

Function to read in, write, and perform any mathematical operation on BDFs.

%% DESCRIPTION:
%
% Performs channel operations on Biosemi Data Files (BDFs). This proved
% useful when files are too big to open in their entirety due to high
% sampling rates or long experiment times.
%
% At its core, this function operates much as bdf_trim did, but in a much
% more flexible way. That is, this function can be used to trim files or
% perform more complex operations, like averaging over channels, etc.
%
% INPUT:
%
% IN: string, path to original BDF.
% OUT: string, path to trimmed BDF.
% CHANOPS: cell array, each element contains a mathematical evaluation
% string (e.g. '(A1 + A2)./2' to average channels A1 and A2).
% Note that channel names in CHANOPS must match the channel
% names in the BDF precisely.
%
% *Note*: Function assumes all channels included in a given
% operation -- that is, an element of the cell array -- are
% of the same transducer type and sampling rate. A safe
% assumption for EEG, but could be a problem for other
% applications.
% OCHLAB: cell array, output channel names. Must be the same length as
% CHANOPS. (optional input)
%
% OUTPUT:
%
% HDR: structure with the following fields
% IDCODE: identification code (8 bytes)
% LSID: local subject identification (80 bytes)
% LRID: local recording identification (80 bytes)
% SDATE: start date (8 bytes)
% STIME: start time (8 bytes)
% NBYTES: number of bytes in header (8 bytes)
% VDFRM: version data format (44 bytes; "24BIT" for BDF)
% NDREC: number of data records (8 bytes)
% DDREC: duration of data record in seconds (8 bytes)
% NCHAN: number of channels (4 bytes)
% CHLAB: channel labels (Nx16 bytes)
% TTYPE: transducer type (Nx80bytes)
% PHDIM: physical dimension of channels (Nx8 bytes)
% PHMIN: physical minimum in units (Nx8 bytes)
% PHMAX: physical maximim in units (Nx8bytes)
% DGMIN: digital minimum (Nx8 bytes)
% DGMAX: digital maximum (Nx8 bytes)
% PRFLT: prefiltering (Nx80 bytes)
% NSAMP: Number of samples in each data record (i.e. sample rate if
% DDREC=1 sec; Nx8 bytes)
% RESRV: reservered (Nx32 bytes)
%
% HEADER: header string of INput file.
% HEADEROUT: header string of OUTput file.
% DATA: Operated data.
%
%
% NOTES:
%
% 120626CWB: Function tested to read and write file as is (first pass
% sanity check). Linux command line "diff" function shows
% that original file is identical to output from
% bdf_ChanOps.m.
%
% IN='s3188/eeg/s3188_PEABR_Exp02C (6.79 msec).bdf';
% OUT='s3188/eeg/s3188_bdf_chanops.bdf';
% CHANOPS={'A1' 'A2' 'A3' 'A4' 'A5' 'A6' 'EXG1' 'EXG2' 'EXG3' 'EXG4' 'Status'};
% OCHLAB={'A1' 'A2' 'A3' 'A4' 'A5' 'A6' 'EXG1' 'EXG2' 'EXG3' 'EXG4' 'Status'};
%
% 120704CWB: Substantial rewrite of function, including addition of
% several smaller functions (e.g. BDF2DATA). Ran the command
% above to read in a file and rewrite it with no changes
% made. This led to no differences using the "diff" command.
%
% 120704CWB: Testing with average of first 6 channels and a single
% channel reference.
% IN='s3188/eeg/s3188_PEABR_Exp02C (6.79 msec).bdf';
% OUT='s3188/eeg/s3188_bdf_chanops.bdf';
% CHANOPS={'(A1+A2+A3+A4+A5+A6)./6' 'EXG1' 'Status'};
% OCHLAB={'Vertex' 'Reference' 'Status'};
%
% These data look great, but will NOT match EEGLAB perfectly.
% I fiddled around with this and it
% seems this is PROBABLY because BDFs have an inherent
% maximum resolution of ~0.0312 uV (at 24 bit resolution),
% while MATLAB has much greater precision when doing
% averaging, even with SINGLE precision.
%
% Bishop, Christopher W.
% UC Davis
% Miller Lab 2011
% [e-mail]