XMOS xsoftip Audio BiQuad Function Library

Transcription

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

2 XMOS xsoftip Audio BiQuad Function Library 2/12 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 Receive Functions Transmit Functions DSP Processing Functions Programming Guide Key Files Usage Demo Applications BiQuad Application For slicekit Board (app_slicekit_biquad) Makefile Running the application with the Command Line Tools Trouble-shooting Try Other Audio Applications

3 1 Overview This application filters an audio stream using a Digital BiQuad Filter as described here 1. It is implemented in Direct Form 2, which requires only two delay registers. The BiQuad filter is flexible and can be configured in many different ways. For example, Low-Pass, Hi-Pass and so on. 1

4 2 Resource Requirements IN THIS CHAPTER Available Memory Computation 2.1 Available Memory This approximate memory usage for this module is (figures shown in Bytes): codememory: 14K datamemory: 2K 2.2 Computation The BiQuad algorithm uses 6 multiplies/sample on each iteration. It is estimated that 24 multiplies are possible at 48kHz sample rate. This would allow 4 channels of audio to be processed simultaneously.

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_biquad 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_FILT_MODE DEF_SAMP_FREQ Default Filter Mode LO_PASS. DEF_SIG_FREQ Default Sample Frequency (In Hz) QUAL_BITS Default Significant Filter Frequency (In Hz) DEF_QUAL_FACT Number of bits used to scale Quality-factor 8. Default Quality-factor of 1, scaled by (1 < QUAL_BITS). 4.2 Functions Data Types S32_T 32-bit types Data Structures BIQUAD_PARAM_TAG

7 XMOS xsoftip Audio BiQuad Function Library 7/12 Structure containing BiQuad parameters. Fields FILT_MODE_TYP filt_mode S32_T samp_freq S32_T sig_freq S32_T qual Configuration Functions config_biquad_filter() Configure BiQuad filter. Type void config_biquad_filter(s32_t biquad_id, BIQUAD_PARAM_S &cur_param_ps) Parameters biquad_id cur_param_ps // Identifies which BiQuad to use // Reference to structure containing current biquad filter parameters

8 XMOS xsoftip Audio BiQuad Function Library 8/ Receive Functions Transmit Functions DSP Processing Functions use_biquad_filter() Use BiQuad filter on one sample from one channel. Samples are left-aligned signed values. e.g. 24-bit audio will look like 0x (positive) or 0xFF (negative) Type S32_T use_biquad_filter(s32_t biquad_id, S32_T inp_samp, S32_T cur_chan) Parameters biquad_id // Identifies which BiQuad to use inp_samp cur_chan // Unfiltered input sample from channel // current channel Returns The Filtered Output Sample

9 5 Programming Guide IN THIS CHAPTER Key Files Usage 5.1 Key Files biquad_simple.c: Contains C function library biquad_simple.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_biquad_filter() Called to do initial configuration of biquad parameters (e.g. Low-pass). WARNING: This must be called before... use_biquad_filter(), which is called to apply the filter to one audio-sample, designed to be called from an xc file. Note well: After initialization, config_biquad_filter() can be called again as required to re-configure the filter. To set the filter parameters, edit the following defines in the include file module_dsp_biquad/src/biquad_simple.h DEF_FILT_MODE // Default Filter Mode DEF_SAMP_FREQ // Default Sample Frequency DEF_SIG_FREQ // Default Significant Filter Frequency (E.g. Low-pass cut-off) DEF_QUAL_FACT // Default Quality-factor

10 6 Demo Applications IN THIS CHAPTER BiQuad Application For slicekit Board (app_slicekit_biquad) Try Other Audio Applications 6.1 BiQuad Application For slicekit Board (app_slicekit_biquad) To get started with this application, run through the instructions in the BiQuad Filter quickstart guide. This application uses module_dsp_biquad to apply a filter to 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) Makefile The Makefile is found in the top-level directory of the application (e.g. app_slicekit_biquad) 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_BIQUAD_CHANS = Running the application with the Command Line Tools In the top-level directory of the application (e.g. app_slicekit_biquad) type xmake clean xmake all Connect the board to your PC using an xtag-2 To start the demo type xrun io bin/app_slicekit_biquad.xe

11 XMOS xsoftip Audio BiQuad Function Library 11/12 When listening to the output audio at 48kHz sample rate, you should hear the following... About 8 seconds of the effect (i.e. low-pass audio), followed by About 8 seconds of the dry (un-effected) signal (i.e. quieter audio) Each time the effect is chosen, the filter switches to a different mode. Currently the following 6 modes are supported: LO_PASS, // Low Pass Filter HI_PASS, // High Pass Filter BAND_PASS, // Band Pass Filter BAND_STOP, // Band Stop (Notch) Filter ALL_PASS, // Phase-Shift Filter CUSTOM, // Custom Filter 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. The filter may produce output audio that is louder than the input, especially when high value for Quality_Factor are selected. This in turn may produce audible distortion in the output audio. If this occurs, try one of the following: Turning down the volume of the audio source (i.e. the volume level input to the application), Reduce the value of DEF_QUAL_FACT 6.2 Try Other Audio Applications Some of the other audio applications are app_slicekit_loudness, app_slicekit_short_delay, app_slicekit_short_reverb. The loudness application increases the perceived loudness, without increasing the maximum volume. Loudness slicekit Audio Demo The short delay application creates a multiple echo effect, by storing audio in local memory. Short-Delay slicekit Audio Demo 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

12 XMOS xsoftip Audio BiQuad Function Library 12/12 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.