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I've previously shared about podcast quality in terms of bitrate, CBR versus VBR, and LAME versus Fraunhofer(in iTunes). But whatever method you use for encoding still leaves a remaining questions: mono or stereo?
Consider the following five things as you decide whether to publish your podcasts in mono or stereo.
1. File size
We now have smartphones and portable audio players with 32 GB or more storage. But this doesn't mean file size should be ignored. A stereo file will always be twice the size of a mono file, when the same quality is used (more on quality later).
- LibSyn and BluBrry offer limited-space media hosting. a 45 MB file will instantly fill up a 50 MB LibSyn plan.
- iPhone and other smartphones on some carriers have a 3G download limit of around 20 MB. A 25 MB podcast file won't download through this 3G.
- Local storage for your raw files may be limited. A raw stereo recording of an hour will be about 620 MB. The same recording in mono will be 310 MB. This adds up quickly when you start working with high-quality raw audio in Audacity, Audition, or similar.
For some hosting places, bandwidth isn't an issue. LibSyn and Blubrry provide unlimited bandwidth for the limited storage they offer.
But if you host your media files with another host, such as Amazon S3 or even your own web host, bandwidth usage may become an issue.
In November, Noodle.mx Network uses 2.2 terabytes (TB) of bandwidth to serve mostly stereo podcast episodes. This would cost more than $200 with Amazon S3. But if all of those episodes were mono, I would have used only 1.1 TB, resulting in a 50% split of the Amazon S3 bill if I hosted my media with them.
3. Download speed
The USA is actually quite behind in average Internet bandwidth. While “broadband” is available in most of the USA, the speeds greatly vary. Some areas charge $30–$40 per month for around 1 mbps (megabit per second) download. In the greater Cincinnati area, I recently tested 30 mbps cable connections and have friends on even faster.
But whatever the connection speed, the size of your file will affect how fast your episode downloads to your listeners. You may think nothing of a 60 MB file. But would you listeners appreciate a podcast that downloads twice as fast as it used to?
4. Sound quality
Depending on the encoding program you use, mono versus stereo may present some confusion.
- Audacity with LAME will apply your selected bitrate to however many channels you have. Thus, a quality setting of 128 kbps will return the same file size for mono or stereo. If you use Audacity with LAME (not recommended), cut the quality in half when exporting as mono.
- iTunes or other programs with Fraunhofer will properly apply the same level of quality to your channels. A mono file gets 64 kbps for the one channel. A stereo file gets the same quality for each of the two channels, so you end up with 128 kbps. These programs will automatically split the file size without your having to change anything else when you switch to mono.
So when you make a direct comparison of a 64 kbps mono file to a 128 kbps stereo file, do you notice much of a difference? Yes, there is some. Stereo will sound more “surrounding”; mono will sound more centered and “direct.” While stereo may seem better, most listeners may not notice the difference, especially if your podcast is almost entirely voice.
Even if you have music or sound effects, the quality will usually seem just as acceptable in mono. But if you podcast audio dramas, then stereo will be a lot more important as you have to communicate location for some voices or sound effects, or you need that “surrounding” feel to the audio.
If you're a vocal podcast, please do not split the voices, even partially, between left and right channels.
I like listening to podcasts throughout the day. I may be playing them through my studio speakers or walking around with earbuds in my ears. My wife Jenny will sometimes need my attention and she'll have to either yell loudly or come find me before she has any of my attention. This is because I often wear my earphones in both ears. But I can't keep doing that because I need to be available to my wife or others who may be around. And I'm not the only podcast listener like this.
Many podcast-listeners may listen through only one ear using earbuds or Bluetooth headsets. These listeners get no benefit from stereo audio. But if you have any stereo effects, these listeners will miss them if they listen through only a single ear.
Your listeners are the most important in this. While we podcasters may think stereo sounds so much better, or we have our nice 50 mbps Internet connections on a home PC, our listeners may not be in the same place. Do what's best for the listeners, not just what's best for you.
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I am not a podcast producer, but am an avid podcast listener. I TOTALLY AGREE with your point about not spliting voices between the left & right channel. I don't run across this a lot, but I have a few times, usually when two podcasters are at different locations, maybe recording via Skype.
Anyway, this process of having different voices in different ears makes a podcast almost un-listenable. I spend a lot of my listening time with the ear-buds or headphones in just one ear, and obviously that makes it impossible to listen to a podcast produced in this format.
Again, I just wanted to give the listener's perspective on that very helpful piece of advice.
Thanks for the perspective, Alan! I’ve heard many podcasts like this and it was unbearable.
I almost totally agree with your post / podcast: yes you should work in mono most of the time (if you are recording a “mostly speech” podcast where the localization of speakers is not important – ie. not audio-dramas). Two additional reasons for this would be:
– putting the two speakers (interviewer – interviewee) on different channels (left-right) can be surprising and not in a pleasant way (I observed that when I listen to these kinds of podcast on the street I have the feeling that somebody on the street is talking to me – a feeling which I don’t like and which I don’t get if the audio is centered)
– sometimes my cheap earphones give up their ghost partially and as such I can only hear one channel until I can be bothered to get a new earphone
However I would make slightly different recommendations:
– Work in mono but encode in Joint Stereo – Joint Stereo means that it encodes one track + the differences relative to that track from the second track. Given that you use mono as the input, there will be no differences, thus the filesize will be identical to the mono case, but it will work better with some exotic (read: cheap) players.
– Never record more channels than the physical device has. Ie. if you are using a mono microphone (as most mics are) don’t record stereo.
– Use standard sampling frequencies (22.05 KHz or 44.1 KHz) – others won’t work well with exotic players
– Use CBR 64 Kbps Joint Stereo encoding. Lower bitrate might save you some space / bandwith (as would VBR), but it’s not compatible with exotic / cheap players.
I had to test this and I found that, as I suspected, “Joint Stereo” is not possible on mono files. Most of the benefits of podcasting in mono (file size, bandwidth, download speed, etc.) are dependent on single-channel audio.
Yes, Joint Stereo is the most compatible. This is why PowerPress will present warnings in its absence. But I think the large benefits outweigh the minor incompatibilities with very few players. As of yet, I’ve never heard a complaint that my files wouldn’t play.
Yup, mono’s the way to go for most voice-based podcasts. I tended to use a bit rate of 96kb instead of 64kb when I was encoding shows, just because I felt the audio was a little less noisy that way, but it did add a third to the file size.
What program were you using to make your mono MP3s? IF Audacity or LAME, then it makes sense that it would sound “noisy,” because around 64 kbps is when LAME at CBR starts to fail quality.
I’m a newbie to audio.
I have just bought a portable audio recorder with two fixed mics. (Olympus LS-5) Assuming (I know its overkill) I recorded at or near the highest stereo quality 96kHz/2424 bit (I understand the stereo/file size/voice split probs discussed already) and I want to output from Audacity at 44.1kHz/24 bit (or 16??)mono.? Check: What is the best output for compatibility rather than just file size? Will I hit serious probs in Audacity with re-sampling and converting to mono either technically or more likely in terms of quality/errors?
My podcast will be outdoors and I do like the stereo sound I’m getting. I can record in 44.1kHz/24/16 bit mono from the outset…… I’m guessing I should stick with that and avoid making life more difficult? My instinct though was to capture the very best signal at the start hence the question. I’m a new subscriber and have consumed the first 7 episodes so it will take me a long time to catch up 🙂
Thanks a million for the podcast.
Good question, Kevin!
Unless you making a movie or recording music for a published album, I think anything higher than 44.1 KHz at 16 bit is unnecessarily high.
I’ve been following your advice to create mono files based on this episode. Today I got a warning from PowerPress not to do mono. Here’s the explanation from their site (http://create.blubrry.com/resources/powerpress/using-powerpress/warning-messages-explained/):
“Warning: Channel Mode ‘mono’
Blubrry PowerPress checks that your mp3 media is either in ‘stereo’ or ‘joint stereo’ for maximum player compatibility.
Web (Flash) based media players and some portable media players
require either ‘Stereo’ or ‘Joint Stereo’ for proper playback. Playback
typically fails instantly in players that do not support ‘Mono’. To
reach the widest audience possible, we recommend using ‘Joint Stereo’
when creating your mp3 media. Joint Stereo and Mono result in the same
file size, so switching from ‘Mono’ to ‘Joint Stereo’ should not be an
issue if file size is a concern.
Values other than these noted may result in media files that are not compatible with some media players and web flash players.”
I went into my Adobe Audition and I have no idea how to create a Joint Stereo file as they suggest. How can I do and should I do it?
Thanks for all your help!
This isn’t an issue anymore. You must be running an old version of PowerPress because they removed this warning.
According to WordPress I am up to date. Perhaps I should uninstall and then reinstall? Will that mess up all my audio files?
It should be version 5.0.2.
But in any case, you can ignore the warning about mono files.
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