XMOS xsoftip Audio Delay-line Function Library

Transcription

1 XMOS xsoftip Audio Delay-line Function Library Document Number: Publication Date: 2014/4/16 XMOS 2014, All Rights Reserved.

2 XMOS xsoftip Audio Delay-line Function Library 2/11 Table of Contents 1 Overview 3 2 Resource Requirements Available Memory Computation Evaluation Platforms Recommended Hardware slicekit Demonstration Applications Stand Alone Demo Reverb Demo API Configuration Defines Functions Data Types Data Structures Configuration Functions DSP Processing Functions Programming Guide Key Files Usage Demo Applications Short-Delay Application For slicekit Board (app_slicekit_short_delay) Makefile Running the application with the Command Line Tools Trouble-shooting Try Other Audio Applications

3 1 Overview This function library can be used to create multiple echoes by feeding the input audio stream into a delay-line. The delay-line returns a set of delayed outputs (taps), with the number of taps being configurable. The delay-line uses only local memory, so only short delays up to 12,000 samples are possible. For longer delays see the Audio Long Delay Function Library.

4 2 Resource Requirements IN THIS CHAPTER Available Memory Computation 2.1 Available Memory This application uses variable amounts of memory depending on the size of the delay-line, and the number of channels being processed. A MEM_SAMPS definition is used to indicate the amount of memory available for the delay-line. Currently this is set at samples, which uses almost all the available memory on Tile_0. This approximate memory usage for this module is (figures shown in Bytes): codememory: 5K datamemory: 49K 2.2 Computation The Delay-line uses no multiplies. So far, a maximum of 4 delay taps have been used successfully, each on 4 channels. By inspecting timings the processing time for one tap is about 80 cycles. For a 48 khz sample rate and 500 MHz processor, this would allow about 100 taps/sample/channel.

5 3 Evaluation Platforms IN THIS CHAPTER Recommended Hardware Demonstration Applications 3.1 Recommended Hardware slicekit This module may be evaluated using the slicekit Modular Development Platform, available from digikey. Minimum Required board SKUs are: XP-SKC-L16 (slicekit L16 Core Board) plus XA-SK-AUDIO plus XA-SK-XTAG2 (slicekit xtag adaptor) 3.2 Demonstration Applications Stand Alone Demo Example stand-alone usage of this module can be found within the xsoftip suite as follows: Package: sw_audio_effects Application: app_slicekit_short_delay Reverb Demo This module is used in the app_slicekit_short_reverb example application which shows how the module is deployed within the context of a more complex audio processing application. Note that in addition to the recommended hardware above, the XA-SK-SDRAM slicecard will also be required, since this application buffers more audio samples than can be accommodated in the free internal SRAM of the xcore Tile. Package: sw_audio_effects Application: app_slicekit_short_reverb

6 4 API IN THIS CHAPTER Configuration Defines Functions 4.1 Configuration Defines DEF_SAMP_FREQ MEM_SAMPS Default Sample Frequency (In Hz): Memory available to configure delay buffers (in samples). Adjust to suit platform: Functions Data Types S32_T 32-bit types Data Structures DELAY_PARAM_TAG Structure containing Delay-line parameters. Fields S32_T us_delays S32_T num S32_T freq

7 XMOS xsoftip Audio Delay-line Function Library 7/ Configuration Functions config_delay_line() Configure delay_line parameters. NB Must be called before use_delay_line. Type void config_delay_line(delay_param_s &cur_param_s) Parameters cur_param_s DSP Processing Functions use_delay_line() // Reference to structure containing delay-line parameters Exercise delay-line for one input sample. NB Must have previously called config_delay_line. Samples are left-aligned signed values. e.g. 24-bit audio will look like 0x (positive) or 0xFF (negative) Type void use_delay_line(s32_t out_samps[], S32_T inp_samp, S32_T cur_chan) Parameters out_samps[] // array of delayed output samples at channel precision inp_samp cur_chan // Input Sample // current channel Returns The delayed output sample

8 5 Programming Guide IN THIS CHAPTER Key Files Usage 5.1 Key Files delay_line.c: Contains C function library delay_line.h: Header file for C function library 5.2 Usage There are 2 functions in the C library, designed to be called from an xc file. config_delay() Called to do initial configuration of delay parameters (e.g. delay offsets). WARNING: This must be called before... use_delay() Called to apply set of delays to one audio-sample, designed to be called from an xc file. Note, after initialization, config_delay() can be called again as required to reconfigure the delay offsets. Delays are set in microseconds in the us_delays field of the DELAY_PARAM_S structure.

9 6 Demo Applications IN THIS CHAPTER Short-Delay Application For slicekit Board (app_slicekit_short_delay) Try Other Audio Applications Before running this demo, it is suggested that you familiarise yourself with the BiQuad Filter slicekit Audio Demo. 6.1 Short-Delay Application For slicekit Board (app_slicekit_short_delay) This application uses module_dsp_short_delay to create a set of delays (or echoes) for an audio-stream, passing through the slicekit Core board. The audio is connected to the Audio Slice board using the following Analogue ports: Input 0/1 (Microphone mini-jack) Output 0/1 (Headphone mini-jack) An intermediate signal is created mixing the input stream with the output of the delay-line, which is set-up to produce 4 different echoes. This intermedate signal is used for the output, but also fed back into the delay-line, to create a potentially infinite set of echoes. In fact the mixing is arranged so that the echoes decay exponentially in amplitude Makefile The Makefile is found in the top-level directory of the application (e.g. app_slicekit_short_delay) The application is for the slicekit Core Board so the TARGET variable needs to be set in the Makefile: e.g TARGET = SLICEKIT-L16.xn The number of channels supported in currently 2 or 4, this is set in auto_conf.h: e.g. NUM_DELAY_CHANS = Running the application with the Command Line Tools In the top-level directory of the application (e.g. app_slicekit_short_delay) type

10 XMOS xsoftip Audio Delay-line Function Library 10/11 xmake clean xmake all Connect the board to your PC using an xtag-2 To start the demo type xrun io bin/app_slicekit_short_delay.xe When listening to the output audio at 48kHz sample rate, you should hear the following... About 8 seconds of the effect (i.e. multiple echoes decaying in amplitude), followed by About 8 seconds of the dry (un-effected) signal. This cycle will repeat indefinitely Trouble-shooting During initialization, and when the system is reconfigured, there may be audible clicks in the audio. This is expected. 6.2 Try Other Audio Applications Some of the other audio applications are app_slicekit_short_reverb and app_slicekit_long_delay. The short reverb application is an example of a more complex application running 4 cores, and combining the biquad, loudness and short-delay modules to create room-sizes up to about 36 meters (for a stereo channel at 48 khz). Short-Reverb slicekit Audio Demo The long delay application creates a set of long delays upto 24 seconds, by storing audio in the SDRAM Memory-Slice. Long-Delay slicekit Audio Demo

11 XMOS xsoftip Audio Delay-line Function Library 11/11 Copyright 2014, All Rights Reserved. Xmos Ltd. is the owner or licensee of this design, code, or Information (collectively, the Information ) and is providing it to you AS IS with no warranty of any kind, express or implied and shall have no liability in relation to its use. Xmos Ltd. makes no representation that the Information, or any particular implementation thereof, is or will be free from any claims of infringement and again, shall have no liability in relation to any such claims. XMOS and the XMOS logo are registered trademarks of Xmos Ltd. in the United Kingdom and other countries, and may not be used without written permission. All other trademarks are property of their respective owners. Where those designations appear in this book, and XMOS was aware of a trademark claim, the designations have been printed with initial capital letters or in all capitals.