Audio quality guidelines for podcast episodes

At RSS.com, all our shows are distributed in MP3 format. MP3 has been the most popular format for digital music files online since the nineties.

MP3 makes files smaller by removing sound information that is very subtle and usually imperceptible, such as frequencies outside the range of human hearing.

A musician or a sound professional may notice very slight changes in quality, but most listeners can't hear any difference between a studio master and a high-quality MP3.

Most consumer devices, such as Bluetooth headphones, earphones, smart speakers, car sound systems, laptop speakers, smartphones and tablets, sound great but aren't built to reproduce audio professionally, so they won't reveal those subtle details anyway.

For all these reasons, MP3 is today the de facto standard for distributing podcasts worldwide.

Within the MP3 format, a few settings shape the final quality, mainly bitrate and sampling rate. As a rule of thumb:

1. The higher the bitrate, the bigger the audio file.
2. The most popular sampling rate for MP3 files is 44.1 kHz.

The size of an MP3 file follows its bitrate, so it's important to find the right balance. You want high-quality episodes that are also small enough to download quickly on any device, including smartphones with limited data plans.

Podcasting is a global medium, and your show can reach listeners all over the world. Smaller files suit emerging markets, where mobile data is still expensive for most people.

So what is the best tradeoff between audio quality and size?

It depends on whether your podcast contains mainly voice (talk-predominant) or mainly music (music-predominant).

Talk-predominant podcasts (most common)

Most podcasts feature one or more people talking for most of the episode, with only short bits of music, such as an intro, an outro and some background music. We call these talk-predominant podcasts, and they make up the majority of podcasts worldwide. We recommend:

• Bitrate between 96 and 128 kbps
• Sampling rate of 44.1 kHz
• 1 channel (mono)

For talk-predominant podcasts, using 1 channel (mono) instead of 2 will most likely make no noticeable difference to the untrained ear. At the same bitrate, a mono file is the same size as a stereo one.

Music-predominant podcasts

If a podcast includes a lot of music, or more music than talk (for example, a show about classical music that plays the pieces it discusses), we call it a music-predominant podcast. We recommend:

• At least 128 kbps
• Sampling rate of 44.1 kHz
• 2 channels (stereo)

The main difference is the second channel. Recorded music often uses stereo to place different sounds or instruments in different channels or speakers.

Audio quality on RSS.com

We follow these guidelines and automatically encode your episodes into MP3 at 128 kbps and 44.1 kHz. We keep the channels you uploaded, so a mono file stays mono.

The bitrate and sample rate are in line with the Apple audio requirements for podcast creators. Encoding does not change loudness, so set it in your mix before you upload. Apple recommends about -16 LKFS, within 1 dB, with true peaks no higher than -1 dBFS. Ads that PAID inserts are set to about -16 LKFS too, so an episode mixed to that level matches their volume. See why inserted ads can sound louder or quieter than your episode.

If you would prefer us not to process your episodes, upload them as constant bitrate (CBR) MP3 files at 128 kbps and 44.1 kHz. They pass through unchanged. A variable bitrate (VBR) MP3 is converted even at 128 kbps.

If your show needs very high audio fidelity, we can host your episodes at 192 kbps or higher. Contact support@rss.com for more information.

Will the ID3 metadata in my MP3 files be maintained?

Yes. RSS.com does not alter or remove the ID3 metadata in your MP3 files when you upload them.

When we encode an episode, we create a new MP3 file and copy all ID3 tags from your original file into it. Your title, artist, album, artwork, episode number and any other embedded metadata stay exactly as they were.

Related: Which audio file formats does RSS.com support? · What is the single podcast episode size limit? · ID3 tag is missing