Icecast - Jun 2005 - icecast sound compressor

Hi,

I searched the Internet to find an answers, but I didn't find anything 
useful, so I'm turning to you, maybe someone has the answer.

I want to make a realtime broadcast from a Linux box. The source is the 
soundcard's line-in, and it sends the stream to an Icecast server.
I would like to have realtime compressor/limiter functionalities on this 
Linux box, so the outgoing signal would be of a good sound-level. The 
stream would be speech mostly.

I searched with Google, but couldn't find a good solution for this exact 
situation.
Can you give me a hint? What software should I use to make my plans?

Thanks for your reply.

Yours,
Jacint

Hi,

It's going to depend a bit on what format you're going to use.

If you plan to stream in ogg vorbis, you can use Ices 2.x and accept PCM 
via standard input.  This means you could run a sox effect or ecasound to 
get and compress the sound from the soundcard before sending it on to ices. 
Ecasound can make use of LADSPA plugins which opens you to a range of 
compressors, such as the SWH compressor plugins which I'm told are pretty 
good.

If you want to do MP3 then I don't have any good ideas so far.  Darkice 
doesn't allow either receiving from standard input or inserting processing 
(i.e. starting a subprocess which it sends audio to and receives audio back 
from), either of which would be useful functions, and I don't know if Ices 
0.x can accept PCM via stdin either.

I'd be interested to know how you go.  I've not looked at the sox 
compression effects lately so they might do the job, don't know.

Geoff.


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Hi,

Thanks for all of you for your replies!
I took a look at every software you mentioned, and ecasound looks the 
best for me with LADSPA and TAP-plugins.
Just for the sake of Google search and maybe some us you may be 
interested, this is the command I'll use for compressing the online ogg 
vorbis broadcast:

ecasound -f 16,1,44100 -i /dev/dsp -eli:2152,20,1000,20,20,0,0,0,0,6 -o 
stdout | ices2 ices.xml

the 2152 LADSPA plugin is TAP Dynamics (M), with compression of 3:1 at 
threshold -35dB (15+20, as the number 6 represents 3:1 compression at 
-15dB) and after-compression-gain +20dB, 20ms attack and 1000ms release 
times. This is radical, but I want to compress speech where the only 
criteria is for the speech to be understandable. (I may change it later.)
(If you install the LADSPA-plugin for xmms and the TAP-plugins, xmms 
tells you the exact order the numbers are used and their meaning.)

In the ices.xml the interesting lines are:

        <input>
            <module>stdinpcm</module>
            <param name="rate">44100</param>
            <param name="channels">1</param>
        </input>

            <encode>
                <nominal-bitrate>32000</nominal-bitrate>
                <samplerate>44100</samplerate>
                <channels>1</channels>
            </encode>

Yours,
Jacint


Geoff Shang wrote:
> Hi,
>
> It's going to depend a bit on what format you're going to use.
>
> If you plan to stream in ogg vorbis, you can use Ices 2.x and accept 
> PCM via standard input.  This means you could run a sox effect or 
> ecasound to get and compress the sound from the soundcard before 
> sending it on to ices. Ecasound can make use of LADSPA plugins which 
> opens you to a range of compressors, such as the SWH compressor 
> plugins which I'm told are pretty good.
>
> If you want to do MP3 then I don't have any good ideas so far.  
> Darkice doesn't allow either receiving from standard input or 
> inserting processing (i.e. starting a subprocess which it sends audio 
> to and receives audio back from), either of which would be useful 
> functions, and I don't know if Ices 0.x can accept PCM via stdin
either.
>
> I'd be interested to know how you go.  I've not looked at the sox 
> compression effects lately so they might do the job, don't know.
>
> Geoff.
>
>