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From: John Rabson <john.rabson@numeo.fr>
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Date: Sun, 16 Oct 2011 10:28:18 +0200
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Subject: Re: LF: Calibrated S/N files
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Andy,

Many thanks.  I find such things very helpful.

John F5VLF

On 15 Oct 2011, at 13:01CEST, Andy Talbot wrote:

> Further to the files I posted a while back of calibrated S/N ratios.
> and voice signal with poor S/N, I've now gone back and verified the
> software and levels, double checking them against each other
> 
> The file      http://www.g4jnt.com/DownLoad/CalibratedNoise.zip
> contains a complete archive of results.
> 
> In there are .WAV files of tones and a CW message at various Signal to
> Noise ratios - all using mathematically generated tones and noise to
> ensure accurate levels.
> 
> There are also several voice files at various S/N ratios.   The
> reference voice file was recorded from BBC Radio 4 a while ago, then
> filtered to the band 300 - 3300Hz to simulate the output from an SSB
> filter.  The mean amplitude over the recording was measured and
> various levels of noise added to generate the files.
> 
> The voice S/N is not defined in the same way as I did the previous
> ones, so can't be directly compared.
> Here I took the amplitude to be the mean rather than just trying to
> estimate the phoneme peaks by measurement on a spectrogram
> 
> The spreadsheet in the .ZIP shows the parameters applied to all file
> and how the values were derived.
> 
> Also included are a number of programmes files for generating .WAV
> files of  single tone and  a CW message, and for adding noise to the
> file at a precise level. and bandpass filtering a .WAV file
> 
> They were written using a rather archaic 16 bit prog language
> (POwerbasic) and will run from a command prompt or by clicking on tthe
> .EXE, but is not the fastest DSP software in existance.    It was far
> easier to do the code in this language that I've used for years and
> had all the routines and progs ready than to port to a more modern
> language.
> Source code is there if you want to check out
> 
> Andy
> www.g4jnt.com
> 
>