Mp3 (MPEG Layer 3) Tips
Making an mp3 is easy, but there are many steps along the way that can lead to a less than desirable mp3 file. Follow these steps and you’re guaranteed to have the most compatible mp3 files for your podcast.
- Do not use a Variable Bit Rate (VBR). Use a fixed bit rate such as 64Kbps, 96Kbps, 128kbps or larger. Read the section Bit Rates in More Detail for more information.
- Use either 22.05Mhz or 44.1Mhz (44.1Mhz is CD quality and recommended) sample rate. Other sample rates will playback in flash-based players incorrectly, typically making you sound like one of the members of the Chipmunks.
- Don’t use free services such as Archive.org for newly released episodes. Free services do not guarantee delivery of large media like a paid Content Delivery Network (CDN) would and they will throttle/kill excessive downloads rather than host your media for free.
- Do not host your media on the same server as your website. The large media file downloads can cause your website to come to a crawl the first few hours your episodes are released.
- Host your media on a server or service that supports byte serving, which is required for downloading to iTunes and other portable devices. An unmodified HTTP/1.1 complaint web server should support byte serving, but depending on the service that may or may not be the case. Blubrry Media Hosting supports byte serving.
- Make sure your web server reports the correct content type for your media file. Mp3 should report as Content-Type “audio/mpeg.” This is typically not a concern, but can explain why the media file does not play in the computer’s media player when downloaded. Blubrry Media Hosting reports the correct media content types.
- Always make sure your files have the appropriate file extensions (e.g. file.mp3), iTunes and many other applications determine the file content type based on the file extension.
- Only use the 26 English letters, 0-9 numbers and underscore/dash characters for file names and folders. Some applications will not capture the special characters, such as dollar signs or commas, correctly from the file name, which could make the saved file unplayable on the target device.
- Never use spaces in your files and folders (same reason as above).
- Make sure you write ID3 tags to the mp3 files so artwork appears during playback on devices and in iTunes.
- Use “Stereo” or “Joint Stereo.” Mono does not play on some devices and in older versions of Flash.
- “Normalize” your audio to make sure each recording has the same volume level. (Use the same normalized level for every episode.)
- Edit and save your audio in the audio editor’s recommended format (not directly as an mp3 as the quality will change) and only export to mp3 when you are done.
Bit Rates in More Detail
The bit rate has a direct collaboration to the mp3′s file size, every increase to the bit rate will increase the size of the file. For example, going from 64 to 128kbps will double the file size. For that reason, it is important to pick the bit rate that is appropriate for the content. See the list below as a guide.
64Kbps – AM radio quality, best for talk only with the exception for speakers who have extreme soft or deep voices.
96Kbps – FM radio quality, best for talk with enough quality to play bumpers and music.
128Kbps – Compact Disk (CD) quality, best for distributing recordings with music.
192Kbps or higher – High quality, typically the amount of quality added is not worth the extra file size.
The values above are a guide and reflect the results using the popular open source Mp3 LAME encoder. Better quality encoders might provide better quality with lower bit rates. Please refer to the software’s manual for recommendations, or experiment with different bit rates until you find the quality you desire.
Never use a Variable Bit Rate (VBR). Depending on how variable the bit rate is configured, it might only play back correctly with the software that created it. For this reason it is best to avoid using a VBR of any type.
Can’t decide recommendation: 128 kbps
Typical File Sizes from Bit Rate
Below is a list of typical recording bit rates and file sizes.
10 minute recording
64 kbps ~ 5MB
96 kbps ~ 8MB
128 kbps ~ 10MB
30 minute recording
64 kbps ~ 15MB
96 kbps ~ 23MB
128 kbps ~ 30MB
1 hour recording
64 kbps ~ 30MB
96 kbps ~ 45MB
128 kbps ~ 60MB
Larger file sizes negatively impact your file hosting costs, while lower bit rates may impact the quality of your recordings. Picking the right bit rate is a balance between quality an what you can afford.
As a rule of thumb, a 64Kbps file is about 0.5MB per minute, a 96Kbps file is about 0.75MB per minute, and a 128Kbps file is about 1MB per minute. If you do decide to use a larger bit rate, remember that playback when streaming from a web page will be further delayed until enough of the file is downloaded, which might make some of your listeners impatient.
Picking the sample rate is quite easy. The sample rate is the number of samples per second, the more samples the clearer the sound will be. If you’re using a cheap microphone or tape recorder for example, using either 22,050 and 44,100 will not make much of a difference. A typical digital video camera or flip type camera will record somewhere between the two sample rates, in that case you want to use 44,100 Khz. Record at CD quality (most of us do), 44,100 Khz will always sound better than 22,050 Khz
Can’t decide recommendation: 44,100 Khz
Mono, Stereo and Joint Stereo
If you have a tip or recommendation, please contact us and we’ll add it to this page.