I have a recording of a radio programme, which I need to compress down to make it suitable for streaming from a website. I have used iTunes to produce .aiff. and .mp3 files from the original .mov file. I can produce very low bitrate mp3 versions of the audio, but 32kbps is about the limit in terms of sound quality. We’d prefer to keep it at least fairly close to the original quality if we can.

Is producing a mono version an option? Is there a clever way to compress the file size even further without sacrificing sound quality?

and help gratefully appreciated, as always.

try asking at kvraudio.com

Download audacity Convert the File To mono. Listen back to check you haven’t lost anything important from the Summing to mono (An Identical signal left and right will sum to zero if one of them is phase inverted!) Then export to MP3 TBH you’ll not retain anything like original quality at less than 128kbs but if it’s all voice and mono 64 may be ok.

Ok, so the 64KB version is currently arond 18MB. Is this ok for streaming? Would a mono version of that be 32kb/9MB or so?

Bearing in mind that some people may be restricted to low bandwidth internet, how does 64kbps translate to how it will stream? Will it buffer a lot? trying to produce a solution that works well for everyone. Is 64kbps ok over 3G phone networks?

A lot depends on where you are streaming from. You might be better looking at your streaming host rather than the quality of your audio file. Some people ‘cheat’ and use empty Youtube video and add the audio but I reckon you might be better going for a podcasting service such as http://www.buzzsprout.com/

Compressability depends on content the only way to find out what size it will be is to try.
What are you streaming from? A dedicated Streaming platform or a dumb link on a web page?

AAC HE might work? It’s AAC tuned for low bitrates, streaming etc.

And yes you can do mono streams, but you might find there is not much benefit as most encoders nowadays will do clever calculations to avoid the need to code two separate streams (L+R)

AAC HE is supported on considerably less devices than MP3. Of course if Mikeconnor knows his target audience can accept that stream it indeed is better.

I think AAC with a variable bit rate is generally reckoned to be the most efficient compression in terms of quality/file size.

The streaming platform isn’t under my control. All i’ve been asked to do is produce a file suitable fro streaming from an edited section of a radio programme. We’re waiting on permission to use it, but that shouldn’t be an issue. We may end up simply linking to the broadcaster’s own archived file anyway. But then the quality and accessibility is out of our hands. We’d like a version to be accessible to people in other countries, for example, which the broadcaster restricts. we may or may not get permission to do this.

So, a mono file at 64kbps will suffice then?

So, a mono file at 64kbps will suffice then?

Technically yes of course. In reality only you can decide. Listen to it, is it acceptable quality? Is your intended target audience covered bandwidth and format wise? I would imaging the streaming provider should give you some guidelines (maybe not in this instance since you’re asking), good platforms will determine the client capabilities and server up the right bit rate on the fly.
It’s not quite as black and white as xxkbs is good xxxkbs bad.

If the audio is just speech based then go for a mono 22.05kHz MP3 in 64 or 32kbps. Also, if you have the option, choose CBR over VBR. Most of the AAC files we convert are layer3 which is the same as mp3 so it wouldn’t alter the filesize massively.
As leffeboy says, it depends on what you are using to stream.

Best thing is to experiment or ask the streaming platform folk what they prefer.

good luck

TRH (sound engineer 17+ years)

^^ What they said.

Goldwave is also an easy to use and free audio file editor that’ll let you have a play with compression..

therealhoops – Member
If the audio is just speech based then go for a mono 22.05kHz MP3 in 64 or 32kbps. Also, if you have the option, choose CBR over VBR. Most of the AAC files we convert are layer3 which is the same as mp3 so it wouldn’t alter the filesize massively.
As leffeboy says, it depends on what you are using to stream.

Best thing is to experiment or ask the streaming platform folk what they prefer.

good luck

TRH (sound engineer 17+ years)

Why CBR out of interest?

Thanks for the advice. I think 64or even 32kbps mono will do the job. Ultimate sound quality isn’t important, it’s more about the content. I understand we can link to the archive on our website, but as content may be limited in other countries, we will be looking for a way round that. I think we may be granted an exception as it is for the purposes of informing people of facts. Bit of a tricky one, but I’m not the one doing the legal stuff fortunately.