[Speex-dev] Sampling Rate

[Dave Findlay]

I am using Speex with 16-bit mono input data at 11025 (so 176kbps in). I
have it configured for ABR of ~8000 and I see compressed data take about
5% of the original size. It sounds pretty decent to me but it depends on
your application.

-----Original Message-----
From: speex-dev-bounces at xiph.org [mailto:speex-dev-bounces at xiph.org] On
Behalf Of Tom Grandgent tgrand-at-canvaslink.com |speex|
Sent: Monday, December 11, 2006 4:49 PM
To: Findlay, Dave
Subject: Re: [Speex-dev] Sampling Rate

Kirk,

Speex was designed for 8kHz, 16kHz, and 32kHz sample rates.  If you
don't use one of these sample rates, you'll be messing up important
assumptions deep within the codec.  Why these sample rates?  It's
telecommunications tradition, rather than PC audio tradition.

If you want an efficient and high quality format for voice chat, try
16kHz with VBR quality 6.  You should see around a 10:1 compression
ratio when someone is talking.  That is, around 25kbps would be a rough
peak using these settings.

If that's too much bandwidth for you, you can cut it by almost half
using VBR quality 2.  (The loss of quality will be noticible to most
people using headsets.  It is less noticible when using speakers.) For
further bandwidth savings you could use 8kHz, but it's too much of a
quality hit to be worth it in my opinion.

Tom

<khaynes at kirkgames.com> wrote:
> 
> Hi,
> 
> I'm attempting to use speex for voice chat in my game.
> 
> I'm capturing audio from the mic using OpenAL 1.1 in 16 bit mono. What

> sample rate is recommended for capturing from the mic? Which would be
> better: 11025 samples per second, or 22050 samples per second of 16 
> bit mono audio with respect to then encoding/decoding it with speex? 
> I'm using 11025 to reduce bandwidth at the moment to capture.
> 
> Given your answer to the above question, what is the most efficient 
> frame size for encoding the samples to speex frames? The sample code 
> uses 160 samples (320 bytes) of 16 bit audio samples, which are then 
> encoded to 200 bytes of encoded data. Is a 30% reduction in data 
> pretty standard? How do I use speex most efficiently?
> 
> Kirk
> 
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