Data Rates for Podcasting – Data rates for Podcasts – Podcast Streaming audio – Audio conversions – Audio transfers for Podcasts
If you have a business, educational or corporate website you might want to take advantage of the increased speed that the internet now allows by producing audio programmes where people can download samples of your programmes, audio classes or educational programmes. This streaming or download distribution of audio content is now often called “podcasting” . Data rates for podcasts will determine the quality of the audio file and the physical size of the file. Basically it’s a compromise between how small you want the file to be (hence easier for people to download) and the quality you are prepared to tolerate. View more details on audio recording and production in our audio section.
There are many conversion software packages available for this type of transfer work and we find that “Switch” which is produced by NCH software maintains a high quality in the converted files. The download format used is typically Mp3, WMA and becoming more popular because of it’s high quality encoding is “flac”. View more information available on podcast production here.
Once you have chosen your preferred audio encoding format then you will want to determine the bit rate. (not to be confused with the “sample rate” of the audio file, eg 44,100 for standard CD audio) As previously mentioned this will affect the overall file size, Mp3 format is very popular for Podcasting and the table below will give you an indication of time, file size and Bit Rate. These data rates are based on Stereo audio file conversion.
|
Minutes |
32 kbps |
96 kbps |
112 kbps |
128 kbps |
192 kbps |
256 kbps |
320 kbps |
|
5 |
1.2Mb |
3.6Mb |
4.2Mb |
4.8Mb |
6.9Mb |
9.6Mb |
12Mb |
|
10 |
2.4Mb |
7.2Mb |
8.4Mb |
9.6Mb |
13.7Mb |
19.2Mb |
24Mb |
|
20 |
4.8Mb |
14.4Mb |
16.8Mb |
19.2Mb |
27.4Mb |
38.4Mb |
48Mb |
|
30 |
7.2Mb |
21.6Mb |
25.2Mb |
28.8Mb |
41.1Mb |
57.6Mb |
72Mb |
|
40 |
9.Mb |
28.8Mb |
33.6Mb |
38.4Mb |
54.8Mb |
76.8Mb |
96Mb |
|
60 |
14.4Mb |
43.2Mb |
50.4Mb |
57.6Mb |
82.2Mb |
115.2Mb |
144Mb |
Mono files will reduce the file size by half, and while this may be ok for voice only programmes, it may impact negatively on music programmes and you should test the results on a sample part of the music before using mono for podcasts.
A one minute stereo podcast in Mp3 format recorded at 44.1kHz with a bit rate of 128kbps will use about 1Mb of data (this equates to a ratio of approx 10:1 over the standard CD audio file size.
Files at this bit rate are also suitable for emailing if you need to get temporary edits approved or for quick reference checks.
As internet connection speeds improve then larger file sizes with improved quality will become increasingly popular (192kHz Mp3s are already being used more often).
When designing podcasts the overall file size should be taken in to account. For example even a low bit rate file of 96kbps could be over 40Mb if the content is 60 minutes long. This can take some time to download on poor connections. A 96kbps file may not be adequate quality for some programme types.
You can view more information on Procopy Podcast production here.
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