FT_FREQSIMULATION
Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help ft_freqsimulation”.
FT_FREQSIMULATION makes simulated data in FieldTrip format. The data is built up from fifferent frequencies and can contain a signal in which the different frequencies interact (i.e. cross-frequency coherent). Different methods are possible to make data with special properties. Use as [data] = ft_freqsimulation(cfg) The configuration options can include cfg.method = The methods are explained in more detail below, but they can be 'superimposed' simply add the contribution of the different frequencies 'broadband' create a single broadband signal component 'phalow_amphigh' phase of low freq correlated with amplitude of high freq 'amplow_amphigh' amplitude of low freq correlated with amplithude of high freq 'phalow_freqhigh' phase of low freq correlated with frequency of high signal 'asymmetric' single signal component with asymmetric positive/negative deflections cfg.output = which channels should be in the output data, can be 'mixed' or 'all' (default = 'all') cfg.randomseed = 'yes' or a number or vector with the seed value (default = 'yes') The number of trials and the time axes of the trials can be specified by cfg.fsample = simulated sample frequency cfg.trllen = length of simulated trials in seconds cfg.numtrl = number of simulated trials or by cfg.time = cell-array with one time axis per trial, which are for example obtained from an existing dataset For each of the methods default parameters are configured to generate example data, including noise. To get full control over the generated data you should explicitely set all parameters involved in the method of your choise. The interpretation of the following signal components depends on the specified method: cfg.s1.freq = frequency of signal 1 cfg.s1.phase = phase (in rad) relative to cosine of signal 1 (default depends on method) = number or 'random' cfg.s1.ampl = amplitude of signal 1 cfg.s2.freq = frequency of signal 2 cfg.s2.phase = phase (in rad) relative to cosine of signal 1 (default depends on method) = number or 'random' cfg.s2.ampl = amplitude of signal 2 cfg.s3.freq = frequency of signal 3 cfg.s3.phase = phase (in rad) relative to cosine of signal 1 (default depends on method) = number or 'random' cfg.s3.ampl = amplitude of signal 3 cfg.s4.freq = frequency of signal 4 cfg.s4.phase = phase (in rad) relative to cosine of signal 1 (default depends on method) = number or 'random' cfg.s4.ampl = amplitude of signal 4 cfg.n1.ampl = root-mean-square amplitude of wide-band signal prior to filtering cfg.n1.bpfreq = [Flow Fhigh] cfg.n2.ampl = root-mean-square amplitude of wide-band signal prior to filtering cfg.n2.bpfreq = [Flow Fhigh] cfg.asymmetry = amount of asymmetry (default = 0, which is none) cfg.noise.ampl = amplitude of noise In the method 'superimposed' the signal contains just the sum of the different frequency contributions: s1: first frequency s2: second frequency s3: third frequency and the output consists of the following channels: 1st channel: mixed signal = s1 + s2 + s3 + noise 2nd channel: s1 3rd channel: s2 4th channel: s3 5th channel: noise In the method 'broadband' the signal contains a the superposition of two broadband signal components, which are created by bandpass filtering a Gaussian noise signal: n1: first broadband signal n2: second broadband signal and the output consists of the following channels: 1st channel: mixed signal = n1 + n2 + noise 2nd channel: n1 3rd channel: n2 4th channel: noise In the method 'phalow_amphigh' the signal is build up of 4 components; s1, s2, s3 and noise: s1: amplitude modulation (AM), frequency of this signal should be lower than s2 s2: second frequency, frequncy that becomes amplitude modulated s3: DC shift of s1, should have frequency of 0 and the output consists of the following channels: 1st channel: mixed signal = (s1 + s3)*s2 + noise, 2nd channel: s1 3rd channel: s2 4th channel: s3 5th channel: noise In the method 'amplow_amphigh' the signal is build up of 5 components; s1, s2, s3, s4 and noise. s1: first frequency s2: second frequency s3: DC shift of s1 and s2, should have frequency of 0 s4: amplitude modulation (AM), frequency of this signal should be lower than s1 and s2 and the output consists of the following channels: 1st channel: mixed signal = (s4 + s3)*s1 + (s4 + s3)*s2 + noise, 2nd channel: s1 3rd channel: s2 4th channel: s3 5th channel: noise 6th channel: s4 7th channel: mixed part 1: (s4 + s3)*s1 8th channel: mixed part 2: (s4 + s3)*s2 In the method 'phalow_freqhigh' a frequency modulated signal is created. signal is build up of 3 components; s1, s2 and noise. s1: represents the base signal that will be modulated s2: signal that will be used for the frequency modulation and the output consists of the following channels: 1st channel: mixed signal = s1.ampl * cos(ins_pha) + noise 2nd channel: s1 3rd channel: s2 4th channel: noise 5th channel: inst_pha_base instantaneous phase of the high (=base) frequency signal s1 6th channel: inst_pha_mod low frequency phase modulation, this is equal to s2 7th channel: inst_pha instantaneous phase, i.e. inst_pha_base + inst_pha_mod In the method 'asymmetric' there is only one periodic signal, but that signal is more peaked for the positive than for the negative deflections. The average of the signal over time is zero. s1: represents the frequency of the base signal and the output consists of the following channels: 1st channel: mixed signal = asymmetric signal + noise 2nd channel: sine wave with base frequency and phase, i.e. s1 3rd channel: asymmetric signal 4th channel: noise See also FT_FREQANALYSIS, FT_TIMELOCKSIMULATION, FT_DIPOLESIMULATION, FT_CONNECTIVITYSIMULATION
