Richard Farrar's Blog

Podcasts are becoming an increasingly popular communication medium, but if you’re thinking of producing a podcast, how do you choose the best bit rate for your podcast and what are the factors to consider in making your decision?

The choice of bit rate for a podcast can be a bit of a balancing act. On the one hand, having high bit rates will give higher perceived audio quality, whilst on the other, they will lead to larger file sizes and hence longer download times for your listeners. So how do you make the right choice?

The Bit Rate Effect

If all this talk of bit rates is leaving you a bit cold, and you’re not quite sure what to make of things, then my previous article on What are bit rates? may help to get you started and point you in the right direction.

Essentially, higher bit rates give improved audio quality, but at the expense of file sizes, which become larger, and larger file sizes lead directly to longer download times, no matter what your internet connection speed is!

So, when trying to decide on the best bit rate for your podcast, you are really going to want to choose the highest bit rate possible, while retaining reasonable file sizes and practical download times for the majority of your listeners.

Factors to Consider

As there is a trade-off between audio quality and file size for your podcast files, this should force you into taking a few points into consideration when deciding on the best bit rate for your podcast. Some key factors to consider are:

• What download speeds do your listeners have?
• How long are your podcasts?
• Are your podcasts predominantly speech?
• Are your podcasts destined for PCs or MP3 players?

Download Speeds

If the majority of your podcast listeners are still using dial-up internet connections (narrowband), or have slower broadband connections, then it may be best to err on the side of caution and use lower bit rates, hence keeping file sizes and thus download times down.

If you’re not sure what connection speed your listeners have, then your website statistics should be able to tell you. If you don’t have any statistics for your website, you can sign up for Google Analytics, a free service that gives you a wealth of statistical information about your website, to help you on your way.

Podcast Duration

If your podcasts tend to be rather lengthy, this may again prompt you into considering lower bit rates to keep file sizes down and reduce download times.

Speech vs Music

People are far more forgiving listening to speech in lower quality than they are for music. For this reason, if your podcast contains a lot of music which is integral to the podcast rather than just filler, it’s probably worth considering higher bit rates.

PCs or MP3 Players

If the majority of your listeners are likely to listen to your podcast on MP3 players rather than a PCs, then again it could be worth considering using lower bit rates to keep file sizes down,  reducing the storage capacity required on the MP3 players.

Typical Bit Rates

All this might sound wonderful and logical, but how do you  translate it to the real world with real numbers?

Unfortunately, there is no such thing as a typical bit rate for a podcast, as they  vary greatly from as low as 32 kbps up to around 128 kbps. As a rough guide to the use of different bit rates however, the following may be helpful:

• 320 kbps – Virtually indistinguishable from original CDs
• 128 kbps – Typical for musical MP3s and quality podcasts
• 64 kbps – Common bit rate for speech podcasts
• 48 kbps – Reasonably common for longer speech podcasts
• 32 kbps – Poor, usually used to reduce download times

British Broadcasting Corporation

The BBC have been broadcasting since 1922 and are generally acknowledged as setting standards in the world of broadcasting. As a rule of thumb, if it’s good enough for the Beeb, the chances are it’s good enough for the likes of you and me!

The BBC have adopted podcasting as a new broadcasting medium and are now heavily into podcasts. As such they have published a range of standards and guidelines for their new media formats.

In summary, the BBC’s recommendations for podcast bit rates are:

• MP3 Mono Speech: 64 kbps, 44.1 kHz, constant bit rate
• MP3 Stereo Music: 128 kbps, 44.1 kHz, constant bit rate

Your Choice

What’s right for the BBC however, may not be right for you. There is no definitive right or wrong, as the choice depends on a number of factors, not least of which is what quality are you happy with putting out?

At the end of the day, you can always change things at a later date. You can use the above recommended bit rates as a good starting point and listen to the feedback from your listeners, re-evaluating the situation in the future if necessary.

Listen for Yourself

Rather than take my word for it, why don’t listen for yourself to the direct effect of bit rates on audio quality, with the following demonstration MP3 tracks, courtesy of Silicon Bay:

• 128 kbps MP3 – MP3 track recorded at 128 kbps (92kB)
• 64 kbps MP3 – MP3 track recorded at 64 kbps (43kB)
• 32 kbps MP3 – MP3 track recorded at 32 kbps (22kB)