Apple strives to create the best experience in Apple Podcasts for your listeners and subscribers. Follow these guidelines to help create a high-quality, distortion-free listening experience using the smallest files sizes possible.
Guidelines for subscriber audio in Apple Podcasts Connect
Apple Podcasts Connect accepts audio with a sampling rate of 44.1 kHz and 16-bit or 24-bit resolution and 96, 176.4, or 192 kHz with 24-bit resolution. Note that if stereo audio source exists, it must be used.
Where stereo source is not available, as may be the case with certain vintage or field recordings, send audio source with two identical channels for left and right. Single-channel audio will not be accepted.
Important: All audio must be generated using a CODEC qualified and approved by Apple.
|Format||Container type||Qualified CODEC|
|Pulse-Code Modulation (PCM)||WAV (.wav)|
|Free Lossless Audio Codec (FLAC)||FLAC (.flac)||FLAC|
Guidelines for RSS feed audio
There are several different types of audio formats to choose from when creating your podcast. To distribute a podcast that can be easily streamed without straining listeners’ bandwidth, your audio content should be encoded or compressed in a format that results in the smallest file size possible. For RSS feeds, we strongly recommend using AAC instead of MP3. When choosing AAC, we recommend using the MP4 format over the ADTS format because MP4 allows for the most-efficient streaming usage and accurate seeking.
When compressing your audio file, pay attention to the sample rate, number of channels, and bit rate. Each of these settings can impact the overall quality of your audio if they are not carefully selected. For example, smaller bit rates will result in smaller, streaming-friendly files which will be transmitted faster and more efficiently but may include audible artifacts, or unwanted sounds in your recording, that can’t be removed at the decoding or playback stage. Larger bit rates will result in larger files and increased audio quality, but those files will require more bandwidth for transmission. The best compromise is to select the appropriate bit rate given the sample rate and the number of channels of content to be encoded. Alternatively, if the bit rate is constrained, the signal might have to be preconditioned. To do so, either reduce the sample rate, for example, 48 to 24 kHz, or reduce the number of channels from stereo to mono, or both.
The table below summarizes the recommended bit rate ranges from the most commonly used sample rates and channel configurations. These bit rates apply to both the AAC and MP3 formats. For the same bit rate, AAC will result in better audio quality.
|Number of channels||22.05/24 kHz||44.1/48 kHz|
|1 (mono)||40–80 kbps||64–128 kbps|
|2 (stereo)||80–160 kbps||128–256 kbps|
When creating your podcast, you’ll also adjust settings for audio levels to ensure a consistent and pleasant listening experience. Your audio settings manage the loudness of your podcast to keep sound within a specific range so that all spoken content is audible and free from distortion. For example, content that is heavily compressed and amplified might be too loud, will lack the dynamic range, and can introduce distortion. Alternatively, content with low audio levels will have dynamic range but will be too quiet, making spoken content inaudible or unintelligible. In either case, a listener might have to adjust the playback volume to a comfortable level.
To prevent such content-driven volume adjustments, we recommend that the audio signals are preconditioned so the overall loudness remains around -16 dB LKFS, with a +/- 1 dB tolerance, and that the true-peak value doesn’t exceed -1 dB FS. The LKFS and true-peak values are calculated according to the ITU-R BS.1770-4 recommendation. The preconditioning steps need to occur before the encoding process. We recommend this because audio compression algorithms typically don’t modify the loudness and might clip the signal if the recommended true-peak value is not respected.
You can embed specific data such as the underlying loudness, dynamic range, and peak-level information of your podcast directly into your audio file. To do so, modify the ID3 tags of an MP3 file or in the header of an MP4 file.
The benefit of having this data available within your file is that it allows playback engines to automatically and precisely adjust levels to a predetermined playback or target level. Apple uses this mechanism via the Sound Check setting in the iOS Music app.
When enabled, content with loudness or Sound Check metadata will consistently have playback levels at -16 dB.