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
>
>
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