When you use Acast, we try to make distributing your podcast as simple and effective as possible. One way we can help with this—whether you are a new podcaster or you have moved to Acast from another podcast host—is by optimizing your podcast audio files.

When it comes to audio, generally speaking, higher quality equates to a better-sounding product. However, higher quality means bigger file sizes. So, at what point is the benefit of improved quality outweighed by file size? To answer that, Acast looks to the listeners—the most important consumer--in delivering a great podcast.

According to the 2018 comprehensive analysis of podcast consumption by Edison Research, almost three quarters of listeners consume podcasts on a mobile device. As a consequence of massive smartphone proliferation and bluetooth audio in cars, enjoying podcasts on the go is easier than ever. It's because of this trend towards mobile consumption that Acast has designed our beautiful podcast websites to work perfectly on smartphones.

However, as anyone who has listened to a podcast in the car or subway can attest, these are not exactly the most "sonically ideal" listening circumstances. The fact is that we are listening in noisy, busy environments, and our audio processing needs to reflect this. For this reason we advise podcasters to pay close attention to ensuring that vocal delivery is very clear, and well compressed to ensure that quieter sections of speech are not drowned out by passing cars or sirens—something that radio professionals have long known.

Because podcasts are relatively long, the file sizes can quickly become problematically large for listeners if they are not encoded at the right settings. Picture this: you have a 500MB data plan (pretty typical in the USA and abroad), and a new podcast episode comes out that is 100MB in size. This could wipe out 20% of your data plan with just a single download! 

Now, sure sometimes, even the most well-optimized files are 100MB, but in our analysis of podcasts currently in the iTunes store, more than half are excessively large—meaning they are delivering hits to listeners data plans without any meaningful improvement in audio quality.

Suppose you have a 1 hour podcast episode. Here's what that means for the audio file that you create, depending on your encoding settings.

As Gizmodo agrees, audio streaming is a potential hazard for massive data consumption:

Going back to those numbers above, it's clear that the bigger files are more of a pain for listeners to download—but they are also supposedly better quality. So the question is: what is the real world impact for listeners? After all, we ideally don't want to make sacrifices in quality or speed—we want speedy delivery of great sounding audio files which don't wipe out our data plans.

Fortunately, our friends at NPR conducted a valuable study, in which they compare human's ability to discern the 'best' audio files from among a mix of bitrates. The conclusion? Most users (i.e. NPR listeners) cannot tell the difference between the 'high-end' and 'low end" encoding rates. 

In particular, the result of the NPR study shows that above 128kbps, increasing the bit rate does not generate a discernible increase in quality. And if you're not improving quality for your listeners, you're just adding to the burden on their cellphone bills. For this reason, when Acast optimizes files, we ensure that the files are encoded as 128kbps MP3 files.

Podcast advertising partners require file standardization for your podcast to be eligible for dynamic ad insertion. In order for ads to be stitched into your audio file, the podcast audio files need to match the encoding of the ad audio file, and the ads are encoded at 128kbps MP3.

No. You absolutely do not. You can upload your files at your preferred bit rate, and Acast will ensure these files are converted and delivered at the optimized rate.