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发板cortex\stm32f10xxx speex library firmware 手册.pdf
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发板cortex\stm32f10xxx speex library firmware 手册.pdf
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October 2008 Rev 2 1/21
AN2812
Application note
Vocoder demonstration using a Speex audio codec
on STM32F101xx and STM32F103xx microcontrollers
Introduction
This application note describes how to implement the codec Speex software on the
STM32F101xx and STM32F103xx microcontrollers to build a vocoder application.
Speex is a free audio codec dedicated to speech encoding and decoding. It provides a high
level of compression with a good quality of sound. That makes it a high-performance
solution for any application using message playback or a voice recorder, like answering
machines, building and home safety systems, intercoms, smart appliances, voice recorders
or walkie-talkies.
www.st.com
Contents AN2812
2/21
Contents
1 Speex codec overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 The vocoder application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1 Vocoder application overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Hardware description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3 Speex codec implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3.1 Speex codec settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3.2 Speex codec optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3.3 Speex codec requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4 Vocoder firmware description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4.1 Playback application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4.2 Record and play application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4.3 Loopback application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
AN2812 List of tables
3/21
List of tables
Table 1. Speex implementation requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Table 2. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
List of figures AN2812
4/21
List of figures
Figure 1. STM32F101xx and STM32F103xx vocoder hardware description . . . . . . . . . . . . . . . . . . . . 6
Figure 2. OLIMEX STM32F103-STK audio input/output stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 3. Playback application flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 4. Record & Play block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Figure 5. Main record application flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Figure 6. Main play application flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Figure 7. TIM3_IRQHandler flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 8. Real-time loopback principle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 9. Loopback flowchart. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 10. TIM2_IRQHandler flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
AN2812 Speex codec overview
5/21
1 Speex codec overview
The Speex codec is an open-source, patent- and royalty-free software dedicated to speech
compression and decompression.
Speex is based on CELP (code-excited linear prediction) and designed to compress voice at
bitrates ranging from 2 to 44 kbps.
The features of Speex include:
– Narrowband (8 kHz), wideband (16 kHz), and ultrawideband (32 kHz) compression in
the same bitstream
– Intensity stereo encoding
– Packet loss concealment
– Variable bitrate operation (VBR)
– Voice activity detection (VAD)
– Discontinuous transmission (DTX)
– Fixed-point port
– Acoustic echo canceller
– Noise suppression
Note that Speex has a number of features that are not present in other codecs, such as
intensity stereo encoding, integration of multiple sampling rates in the same bitstream
(embedded coding), and a VBR mode.
For more information about the Speex codec, please refer to the Speex website:
www.speex.org.
Note: This application note was developed with the release 1.2rc1 of the Speex codec.
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