| <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> |
| <HTML> |
| |
| <HEAD> |
| <TITLE> |
| Secret Rabbit Code (aka libsamplerate) |
| </TITLE> |
| <META NAME="Author" CONTENT="Erik de Castro Lopo (erikd AT mega-nerd DOT com)"> |
| <META NAME="Version" CONTENT="libsamplerate-0.1.8"> |
| <META NAME="Description" CONTENT="The Secret Rabbit Code Home Page"> |
| <META NAME="Keywords" CONTENT="libsamplerate sound resample audio dsp Linux"> |
| <LINK REL=StyleSheet HREF="SRC.css" TYPE="text/css" MEDIA="all"> |
| </HEAD> |
| |
| <BODY TEXT="#FFFFFF" BGCOLOR="#000000" LINK="#FB1465" VLINK="#FB1465" ALINK="#FB1465"> |
| <!-- pepper --> |
| <CENTER> |
| <IMG SRC="SRC.png" HEIGHT=100 WIDTH=760 ALT="SRC.png"> |
| </CENTER> |
| <!-- pepper --> |
| <BR> |
| <!-- pepper --> |
| <TABLE ALIGN="center" WIDTH="98%"> |
| <TR> |
| <TD VALIGN="top"> |
| <BR> |
| <DIV CLASS="nav"> |
| <BR> |
| <A HREF="index.html">Home</A><BR> |
| <BR> |
| <A HREF="api_simple.html">Simple API</A><BR> |
| <A HREF="api_full.html">Full API</A><BR> |
| <A HREF="api_misc.html#ErrorReporting">Error Handling</A><BR> |
| <A HREF="api_misc.html">Miscellaneous</A><BR> |
| <BR> |
| <DIV CLASS="block"> |
| Author :<BR>Erik de Castro Lopo |
| <!-- pepper --> |
| <BR><BR> |
| <!-- pepper --> |
| |
| </DIV> |
| <IMG SRC= |
| "/cgi-bin/Count.cgi?ft=6|frgb=55;55;55|tr=0|md=6|dd=B|st=1|sh=1|df=src_api.dat" |
| HEIGHT=30 WIDTH=100 ALT="counter.gif"> |
| </DIV> |
| |
| </TD> |
| <!-- pepper --> |
| <!-- ######################################################################## --> |
| <!-- pepper --> |
| <TD VALIGN="top"> |
| <DIV CLASS="block"> |
| |
| <H1><B>Miscellaneous API Documentation</B></H1> |
| <A NAME="ErrorReporting"></A> |
| <H3><BR>Error Reporting</H3> |
| <P> |
| Most of the API functions either return an integer error (ie <B>src_simple</B> |
| and <B>src_process</B>) or return an integer error value via an int pointer |
| parameter (<B>src_new</B>). |
| These integer error values can be converted into a human readable text strings by |
| calling the function: |
| </P> |
| <PRE> |
| const char* src_strerror (int error) ; |
| </PRE> |
| <P> |
| which will return an error string for valid error numbers, the string "No Error" |
| for an error value of zero or a NULL pointer if no error message has been defined |
| for that error value. |
| </P> |
| |
| <A NAME="Converters"></A> |
| <H3><BR>Converters</H3> |
| <P> |
| Secret Rabbit Code has a number of different converters which can be selected |
| using the <B>converter_type</B> parameter when calling <B>src_simple</B> or |
| <b>src_new</B>. |
| Currently, the five converters available are: |
| </P> |
| <PRE> |
| enum |
| { |
| SRC_SINC_BEST_QUALITY = 0, |
| SRC_SINC_MEDIUM_QUALITY = 1, |
| SRC_SINC_FASTEST = 2, |
| SRC_ZERO_ORDER_HOLD = 3, |
| SRC_LINEAR = 4 |
| } ; |
| </PRE> |
| <P> |
| As new converters are added, they will given a number corresponding to the |
| next inetger. |
| </P> |
| |
| <P> |
| The details of these converters are as follows: |
| </P> |
| <UL> |
| <LI> <B>SRC_SINC_BEST_QUALITY</B> - This is a bandlimited interpolator derived |
| from the mathematical <B>sinc</B> function and this is the highest |
| quality sinc based converter, providing a worst case Signal-to-Noise |
| Ratio (SNR) of 97 decibels (dB) at a bandwidth of 97%. |
| All three SRC_SINC_* converters are based on the techniques of |
| <A HREF="http://ccrma-www.stanford.edu/~jos/resample/">Julius O. Smith</A> |
| although this code was developed independantly. |
| <LI> <B>SRC_SINC_MEDIUM_QUALITY</B> - This is another bandlimited interpolator |
| much like the previous one. It has an SNR of 97dB and a bandwidth of 90%. |
| The speed of the conversion is much faster than the previous one. |
| <LI> <B>SRC_SINC_FASTEST</B> - This is the fastest bandlimited interpolator and |
| has an SNR of 97dB and a bandwidth of 80%. |
| <LI><B>SRC_ZERO_ORDER_HOLD</B> - A Zero Order Hold converter (interpolated value |
| is equal to the last value). The quality is poor but the conversion speed is |
| blindlingly fast. |
| <li><b>SRC_LINEAR</b> - A linear converter. Again the quality is poor, but the |
| conversion speed is blindingly fast. |
| </UL> |
| <P> |
| There are two functions that give either a (text string) name or description |
| for each converter: |
| </P> |
| <PRE> |
| const char *src_get_name (int converter_type) ; |
| const char *src_get_description (int converter_type) ; |
| </PRE> |
| <P> |
| The name will typically be a short string for use in a dialog box, while the |
| description string is longer. |
| </P> |
| <P> |
| Both of these functions return a NULL pointer if there is no converter for the |
| given <B>converter_type</B> value. |
| Since the converters have consecutive <B>converter_type</B> values, the caller |
| is easily able to figure out the number of converters at run time. |
| This enables a binary dynamically linked against an old version of the library |
| to know about converters from later versions of the library as they become |
| available. |
| </P> |
| |
| <A NAME="SRC_DATA"></A> |
| <H3><BR>SRC_DATA</H3> |
| <P> |
| Both the simple and the full featured versions of the API use the <B>SRC_DATA</B> |
| struct to pass audio and control data into the sample rate converter. |
| This struct is defined as: |
| </P> |
| <PRE> |
| typedef struct |
| { float *data_in, *data_out ; |
| |
| long input_frames, output_frames ; |
| long input_frames_used, output_frames_gen ; |
| |
| int end_of_input ; |
| |
| double src_ratio ; |
| } SRC_DATA ; |
| </PRE> |
| <P> |
| The <B>data_in</B> pointer is used to pass audio data into the converter while the |
| <B>data_out</B> pointer supplies the converter with an array to hold the converter's |
| output. |
| For a converter which has been configured for mulitchannel operation, these pointers |
| need to point to a single array of interleaved data. |
| </P> |
| <P> |
| The <B>input_frames</B> and <B>output_frames</B> fields supply the converter with |
| the lengths of the arrays (in frames) pointed to by the <B>data_in</B> and |
| <b>data_out</B> pointers respectively. |
| For monophinc data, these values would indicate the length of the arrays while |
| for multi channel data these values would be equal to the the length of the array |
| divided by the number of channels. |
| </P> |
| |
| <P> |
| The <B>end_of_input</B> field is only used when the sample rate converter is used |
| by calling the <B>src_process</B> function. |
| In this case it should be set to zero if more buffers are to be passed to the |
| converter and 1 if the current buffer is the last. |
| </P> |
| <P> |
| Finally, the <B>src_ratio</B> field specifies the conversion ratio defined as |
| the input sample rate divided by the output sample rate. |
| For a connected set of buffers, this value can be varies on each call to |
| <B>src_process</B> resulting in a time varying sample rate conversion |
| process. |
| For time varying sample rate conversions, the ratio will be linearly |
| interpolated between the <B>src_ratio</B> value of the previous call |
| to <B>src_process</B> and the value for the current call. |
| </P> |
| <P> |
| The <B>input_frames_used</B> and <B>output_frames_gen</B> fields are set by the |
| converter to inform the caller of the number of frames consumed from the |
| <B>data_in</B> array and the number of frames generated in the <B>data_out</B> |
| array respectively. |
| These values are for the current call to <B>src_process</B> only. |
| </P> |
| |
| <A NAME="Aux"></A> |
| <H3><BR>Auxillary Functions</H3> |
| <P> |
| There are four auxillary functions for converting arrays of float data |
| to and from short or int data. |
| These functions are defined as: |
| </P> |
| <PRE> |
| void src_short_to_float_array (const short *in, float *out, int len) ; |
| void src_float_to_short_array (const float *in, short *out, int len) ; |
| void src_int_to_float_array (const int *in, float *out, int len) ; |
| void src_float_to_int_array (const float *in, int *out, int len) ; |
| </PRE> |
| <P> |
| The float data is assumed to be in the range [-1.0, 1.0] and it is |
| automatically scaled on the conversion to and from float. |
| On the float to short/int conversion path, any data values which would overflow |
| the range of short/int data are clipped. |
| </P> |
| |
| </DIV> |
| </TD></TR> |
| </TABLE> |
| |
| </BODY> |
| </HTML> |
| |