uLaw playback

App_rpt-users
1

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

2

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

From: Angelo Glorioso [mailto:n5uxt@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

From: "Ken" <ke2n@cs.com>
To: <app_rpt-users@ohnosec.org>
Cc: "'Angelo Glorioso'" <n5uxt@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

···

-----Original Message-----
----- Original Message -----
> not damage the sound quality, when used within reason.
>
> 73
>
> Ken
>
>

3

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@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@cs.com>
To: <app_rpt-users@ohnosec.org>
Cc: "'Angelo Glorioso'" <n5uxt@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

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4

Like a few others on the list here, I'm pretty certain there are a few audio/broadcast/radio engineers in the woodpile, so, while it's good enough to use William or Allison via cepstral, there is nothing like actually, should you want, having a professional production or voice to do fixed announcements. I mean, TTS can only go so far, right?

I know it's overkill (anything worth doing is worth doing to excess...;)), but, I have a complete radio (as in broadcast) studio setup at home; full tape (yes, even carts), a-d conversion, processing (dbx, orban) equipment, dynamic, condensor, ribbon mics, etc., and can deliver in multiple formats (mp3, wav, gsm, etc).

Current studio: http://www.wb0yle.com/photos/streaming.jpg

New console I'm restoring to replace the one in the above picture:

Maybe those of us with the skills, on an as-available and casual basis, can help out those who are 'production facilities-challenged?'???

···

On 8/6/13 8:10 AM, Jon Rorke wrote:

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.

--
Bryan
In this world, you must be oh so smart or oh so pleasant.
Well, for years I was smart. I recommend pleasant.
You may quote me.

Sent from my MacBook Pro.