Re: [ecasound] lossless conversion broken?

--- On Sun, 10/31/10, Dan Muresan <danmbox@email-addr-hidden> wrote:

> From: Dan Muresan <danmbox@email-addr-hidden>
> Subject: Re: [ecasound] lossless conversion broken?
> To: "Sergei Steshenko" <sergstesh@email-addr-hidden>
> Cc: "Kai Vehmanen" <kvehmanen@email-addr-hidden>, ecasound-list@email-addr-hidden
> Date: Sunday, October 31, 2010, 10:46 AM
> > For low amplitude signals you
> have quite enough bits in a float, for
> > example, for 5 bit amplitude signal you have all the
> 23 (without sign)
> > bits of float mantissa, so no precision loss occurs.
>
> It doesn't appear to be so, for whatever reason. Try this:
>
> # generate sine wave, -40 db, 100 Hz, 1 second
> sox -t null /dev/null -b 16 sine.wav synth 1.0 sine 100.0
> gain -40
>
> ecaconvert .wav sine.wav
> cmp -l sine.wav sine.wav.wav
> # or better, lfhex -c sine.wav sine.wav.wav
>
> Why are there bit flips for 0x0003 -> 0x0004 or 0x0000
> -> 0x0001? Even
> if you go to -60db you will still see these errors.
>
> But to restate my original question -- does ecasound
> convert to floats
> when recording (with no processing), or does it not? I'm
> not
> interested in lossless conversion using ecasound, but I am
> interestend
> in recording.
>
> -- Dan
>

Here is a small test program:

sergei@email-addr-hidden:~/junk/int_to_float> cat -n int_to_float_and_back.c
     1 #include <stdio.h>
     2
     3 int main()
     4 {
     5 short i, o;
     6 float f;
     7
     8 fprintf(stderr, "sizeof(i)=%u\n", sizeof(i));
     9
    10 for(i = 1; i < 32; i++)
    11 {
    12 f = (float)i;
    13 o = (short)f;
    14 fprintf(stderr, "i=%u f=%g o=%u\n", (unsigned)i, (double)f, (unsigned)o);
    15 }
    16
    17 return 0;
    18 }
sergei@email-addr-hidden:~/junk/int_to_float> ~/AFSWD/install/gcc-4.4.5/binsh/gcc -Wall -Wextra -O2 int_to_float_and_back.c -o int_to_float_and_back
sergei@email-addr-hidden:~/junk/int_to_float> ./int_to_float_and_back
sizeof(i)=2
i=1 f=1 o=1
i=2 f=2 o=2
i=3 f=3 o=3
i=4 f=4 o=4
i=5 f=5 o=5
i=6 f=6 o=6
i=7 f=7 o=7
i=8 f=8 o=8
i=9 f=9 o=9
i=10 f=10 o=10
i=11 f=11 o=11
i=12 f=12 o=12
i=13 f=13 o=13
i=14 f=14 o=14
i=15 f=15 o=15
i=16 f=16 o=16
i=17 f=17 o=17
i=18 f=18 o=18
i=19 f=19 o=19
i=20 f=20 o=20
i=21 f=21 o=21
i=22 f=22 o=22
i=23 f=23 o=23
i=24 f=24 o=24
i=25 f=25 o=25
i=26 f=26 o=26
i=27 f=27 o=27
i=28 f=28 o=28
i=29 f=29 o=29
i=30 f=30 o=30
i=31 f=31 o=31
sergei@email-addr-hidden:~/junk/int_to_float>

-_ no_ loss of precision in case of short -> float -> short conversion.
As it should be.

I don't know which tool on the way has which bugs - for example, some
zero padding might appear, i.e. you might be comparing different
samples. But, as I stated, there are enough bits.

Regards,
  Sergei.

------------------------------------------------------------------------------
Nokia and AT&T present the 2010 Calling All Innovators-North America contest
Create new apps & games for the Nokia N8 for consumers in U.S. and Canada
$10 million total in prizes - $4M cash, 500 devices, nearly $6M in marketing
Develop with Nokia Qt SDK, Web Runtime, or Java and Publish to Ovi Store
http://p.sf.net/sfu/nokia-dev2dev
_______________________________________________
Ecasound-list mailing list
Ecasound-list@email-addr-hidden
https://lists.sourceforge.net/lists/listinfo/ecasound-list
Received on Mon Nov 1 00:15:01 2010