The Podcast Engineering Show

Advanced Audio Coding is designed to be the successor of the MPEG-1 Audio Layer 3, known as MP3 format, which was specified by ISO/IEC in 11172-3 (MPEG-1 Audio) and 13818-3 (MPEG-2 Audio)

The widespread reluctance to even THINK about publishing podcast episodes in any other format than MP3.

.m4a is the most common extension, but not the only extension, used for AAC.

Sound quality: AAC sounds better than MP3 especially when encoded at lower bitrates. This means that your final episode file can be smaller in size and still sound as good or better than MP3.

Chris's experience: "When I convert my .WAV file to MP3 using iZotope RX 7, the resultant MP3 is 0.4 LUFS lower in volume than the original .WAV. Whereas when I convert to .m4a the resulting LUFS level of the .m4a is exactly the same as the original .WAV file. Interesting..."

Compatibility with ad insertion platforms: Rob Greenlee says, "Hey Chris, Most of the platforms that utilized dynamic ad insertion technology, oftentimes require MP3 files only."

TPES episodes that published in .m4a:

• 118 - Chris’s Goody Bag
• 119 - Bryan Entzminger

ID3 Tags: Bryan Entzminger says, "I did a test with an episode. I didn’t like that Libsyn didn’t pull the id3 info from the file (because it’s not an MP3) but that’s not a really big deal."

A few popular shows that use .m4a files:

• Podnews (James Cridland’s show, @ 44.1 kHz so far)
• 60 Sec Torah Byte (Zalman Levin / Podbean 44.1 kHz so far)
• Morning Mantra (Coach MK / Anchor)
• BeyondPodcasting (Allan Tépper’s show, @ 48 kHz)
• Podcast Engineering Show (Barry and Chris’s show, @ 48 kHz)

Technical analysis of top podcasts - James Cridland’s post looking at bitrate. LUFS, mono/stereo, etc.:
https://podnews.net/article/podcast-analysis?utm_source=podnews.net&utm_medium=email&utm_campaign=podnews.net:2019-01-17

Blind tests in the late 1990s showed that AAC demonstrated greater sound quality and transparency than MP3 for files coded at the same bit rate.

Improvements include:

• more sample rates (from 8 to 96 kHz) than MP3 (16 to 48 kHz)
• up to 48 channels (MP3 supports up to two channels in MPEG-1 mode and up to 5.1 channels in MPEG-2 mode)
• higher coding efficiency for stationary signals (AAC uses a blocksize of 1024 or 960 samples, allowing more efficient coding than MP3's 576 sample blocks)
• higher coding accuracy for transient signals (AAC uses a blocksize of 128 or 120 samples, allowing more accurate coding than MP3's 192 sample blocks)
• much better handling of audio frequencies above 16 kHz
• more flexible joint stereo (different methods can be used in different frequency ranges)

*NOTE: NONE of these lists is exhaustive. We did not investigate every single program in existence ;)

Programs that can encode .m4a files:

• iTunes
• Fission (Mac only. Also can tag and create chapters. Allan Tépper’s favorite 1-track audio editor for Mac. Unique because it can also edit lossy formats without generation loss. Can’t save tag data but can copy and paste tag data. Chris was confused because Fission’s tag data doesn’t have a ‘Copyright’ field.)
• Hindenburg Journalist Pro (also can tag and create chapters. Allan Tépper’s favorite multitrack audio editor for conventional computers)
• TwistedWave (Mac and online only. Good program but no playback speed adjustment!)
• Amadeus Pro
• 3rd Party Encoder Plugins (Paul Figgiani suggested Sonnox’s Codec Toolbox ~47 USD and Pro Codec ~400 USD.)

Programs that encode MP3s using the Fraunhofer MP3 Encoder algorithm:

• Adobe Audition
• iTunes (Source: Cliff Ravenscraft on October 27, 2010)
• Windows Media Player (Source: Richard Farrar)

Programs for which you can buy an optional Fraunhofer plugin for US$339.15

• Pro Tools
• Logic
• Cubase
• Nuendo
• Sequoia
• Wavelab

Programs that DON’T use the Fraunhofer MP3 Encoder algorithm:

• Hindenburg
• Reaper
• RX 6, 7