[App_rpt-users] uLaw playback

[Jon Rorke]

When I make my audio files in Audacity, I export to a wav file then I 
export to ulaw.
I then play the wav files back to verify they sound ok.

Works great.

Jon VA3RQ

On 8/6/2013 4:41 AM, Ken wrote:
> If the original wav file is not limited to -6 dBfs (minus 6 dB relative to
> full scale) you can reduce the level "on the fly" by using the lower case
> "v" for volume control.
>
> For example, this reduces the volume to half what it was (-0.5)
>
> sox -v -0.5 -t raw -U -c 1 -r 8000  (etc...)
>
> 73
> Ken
>
>
>> -----Original Message-----
>> From: Angelo Glorioso [mailto:n5uxt at hotmail.com]
>> Sent: Monday, August 05, 2013 10:39 PM
>> To: Ken
>> Subject: Re: uLaw playback
>>
>> Hi Ken,
>>
>> Thanks for your reply. I was able to find the syntax for sox. It worked
> great. It
>> took my wav file and converted it over to ulaw. I used :
>>
>> sox -V n5uxt.wav -r 8000 -c 1 -t ul -w n5uxt.ulaw
>>
>> It was simple and fast.
>>
>> 73, Angelo
>>
>>
>> ----- Original Message -----
>> From: "Ken" <ke2n at cs.com>
>> To: <app_rpt-users at ohnosec.org>
>> Cc: "'Angelo Glorioso'" <n5uxt at hotmail.com>
>> Sent: Monday, August 05, 2013 7:54 PM
>> Subject: uLaw playback
>>
>>
>>> I have read where uLaw produces 14 bit audio (-8159 to +8158
>>> numerically-speaking)  - see Wikipedia on this, for example.
>>>
>>> I am guessing this is the range of numbers used by app_rpt.
>>>
>>> Your 16-bit WAV format is going to produce +/- 32768 (numerically-
>> speaking
>>> again).
>>>
>>> So - you need to divide the WAV output by a factor of 4 to get into the
>>> range that uLaw supports.
>>>
>>> The tutorial on using Audacity for app_rpt:
>>> http://images.ohnosec.org/app-rpt-audacity.pdf  says to normalize at
> -6dB.
>>> You really need to follow that advice to get clean audio.
>>>
>>> "Normalize" will set the loudest sound to the amplitude you select.  If
>>> there are a lot of sound "spikes" in the audio track, you can end up
> with
>>> a
>>> pretty low average sound level.  I have found the best way to fix this
> is
>>> some judicious use of the Audacity "hard limiter" function. It really
> does
>>> not damage the sound quality, when used within reason.
>>>
>>> 73
>>>
>>> Ken
>>>
>>>
>
> _______________________________________________
> App_rpt-users mailing list
> App_rpt-users at ohnosec.org
> http://ohnosec.org/cgi-bin/mailman/listinfo/app_rpt-users
>