I agree with other replies that a 4 kHz sample rate will only capture 2 kHz of the voice spectrum which will result in loss of key sounds, or aliasing that will distort the sound even without any compression/decompression happening.
> "But conversion time to compress 20 ms frame is around 60 ms if I want to use > 3200kbps CODEC" First thing to do is to make sure your 60 ms number is correct and a real limit. How did you measure the 60 ms? Have you turned on your compiler's optimization? How are you obtaining the audio samples? I presume the SAADC on the nRF52. Is that causing any delay other than copying a buffer? Can you use DMA to copy the buffer rather than memcpy()? If you are truly limited by CPU cycles, then consider your choice of codec variant. The 3200 kbps codec will sound better than the 1600 kbps, but the lower bit rate codecs throw away bits that have lesser significance so your CPU will have less number crunching (maths) to do. Lastly, your CPU has SIMD instructions that could really increase your computational power if you have the expertise and time to commit to re-coding all the maths. !!Dean KC4KSU On Jun 12, 2016, at 8:19 AM, Anomadarshi Barua Shuvro wrote: > Hi Glen, > > My hardware bottleneck is for low speed . I am using nRF52 which is a > CortexM4 microcontroller with 64MHz clock speed and 64 KB of RAM . The > problem is if I use 8KHz sampling rate the frame size is 20 ms for 160 > samples ( 3200 kbps) . But conversion time to compress 20 ms frame is around > 60 ms if I want to use 3200kbps CODEC . So I am missing 3 frames for each > compression . So I am using 4 KHz sampling rate because 4KHz sampling rate > would give me 40ms frame for 160 samples . > > > kind regards > Anomadarshi > > On Sun, Jun 12, 2016 at 2:54 PM, glen english <[email protected]> wrote: > Nice one Jereon. > > Anomadarshi, > > where is your hardware bottleneck- why the sample rate limit- help us > understand . > > I thought that if you had a hardware bit rate limit, then going for 8 kHz > sampling and 8 bit samples would be the same information rate as 4 Khz > sampling and 16 bit samples. > > As Jereon says, you will need to format to suit the buffers and structs. > > > > regards > > > On 12/06/2016 10:43 PM, Anomadarshi Barua Shuvro wrote: >> Hi, >> >> Thank you very much...You guys are doing really fantastic jobs.. >> >> kind regards >> Anomadarshi >> >> On Sun, Jun 12, 2016 at 2:23 PM, Jeroen Vreeken <[email protected]> wrote: >> Hi Anomadarshi, >> >> On 06/12/2016 02:11 PM, Anomadarshi Barua Shuvro wrote: >> > Hi Glen, >> > Thank you very much for your reply . I have few confusions. If I would >> > use 8bit resolution per sample , then I would need to change line 3 in >> > the following piece of code , right ? If I would change line 3 to buf >> > = (char*)malloc(nsam*sizeof(char)) , will it work ? I mean do I need >> > to change anything inside of the codec ? >> > >> No, that won't work. >> The codec expects a buffer of shorts. So even if you sample only bytes >> you would still have to convert them to shorts. >> >> This is the prototype of the encode function: >> void codec2_encode(struct CODEC2 *codec2_state, unsigned char * bits, >> short speech_in[]); >> >> It has not changed by your change. >> >> Regards, >> Jeroen >> >> >> ------------------------------------------------------------------------------ >> What NetFlow Analyzer can do for you? Monitors network bandwidth and traffic >> patterns at an interface-level. Reveals which users, apps, and protocols are >> consuming the most bandwidth. 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Make informed decisions using capacity > planning reports. https://ad.doubleclick.net/ddm/clk/305295220;132659582;e > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > ------------------------------------------------------------------------------ > What NetFlow Analyzer can do for you? Monitors network bandwidth and traffic > patterns at an interface-level. Reveals which users, apps, and protocols are > consuming the most bandwidth. Provides multi-vendor support for NetFlow, > J-Flow, sFlow and other flows. Make informed decisions using capacity > planning reports. > https://ad.doubleclick.net/ddm/clk/305295220;132659582;e_______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 ------------------------------------------------------------------------------ What NetFlow Analyzer can do for you? Monitors network bandwidth and traffic patterns at an interface-level. Reveals which users, apps, and protocols are consuming the most bandwidth. Provides multi-vendor support for NetFlow, J-Flow, sFlow and other flows. Make informed decisions using capacity planning reports. https://ad.doubleclick.net/ddm/clk/305295220;132659582;e _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
