(Audio Dsp) Extracting a specific frequency range from a signal

I need a filter written in Ansi C that extracts only certain frequencies within a specific range from an audio signal. ## Deliverables I need a filter written in Ansi C that extracts only certain frequencies within a specific range from an audio signal. The signal will be provided as doubles between -1.0 and 1.0 in Mono only. The API would look something like this: struct freq_state { ... // Any parameters that may need to be stored. }; bool initialize_freq_extractor(freq_state* state, double freq_min, double freq_max, long sample_rate) double process_sample(freq_state* state, double sample) // Processes one sample at a time and returns the output. void free_freq_extractor(freq_state* state) // Only necessary if dynamic memory is allocated, I imagine. The output would be the new signal with all frequencies outside the range of freq_min and freq_max completely removed. Note that if one were to process the same signal several times with different ranges that together span over the entire spectrum (usually 0 hZ to 20 khZ) and then add the different outputs together to form a single signal, that output must be completely transparent (e.g. not differ from the original audio). This basically means that this filter could be used as an equalizer with x number of bands. You may use any existing source code that is in the public domain. This is a work made for hire. 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows? (depending on the nature? of the deliverables): a)? For web sites or? other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software? installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform Ansi C