A Quasi-technical Analysis of the Top Podcasts about Podcasting

Struggling to work out the best settings for your podcast’s technical production? Ever wondered exactly what the top podcasters are doing and how they compare to each other? Wonder no more!

As a little exercise I thought it might be interesting to look at a few of the top podcasts about podcasting to see what their final production quality is like and how they compare to each other.

This following analysis is purely based on the quantifiable aspects of the “final product” of the podcasts and as such aims to be entirely objective. No consideration is given to the actual content of the podcasts, or indeed whether the hosts can actually string together a coherent sentence or not (as it happens they all seem to do remarkably well on this account).

While I’ve tried to be as accurate and methodical in my approach as possible I do not make any claims about its scientific rigour, but hopefully I’ve remained neutral and have explained all of my methods and reasons along the way.

The Top Four Podcasts about Podcasting

For this exercise I chose four podcasts about podcasting that I regularly listen to and the ones I believe are evangelizing podcasting and are, or should be, at the top of their game. They are, in alphabetical order so as to show no bias:

• Podcast Answer Man [PAM] – Cliff J. Ravenscraft
• School of Podcasting [SOP] – David Jackson
• The Audacity to Podcast [TAP] – Daniel J. Lewis
• The Podcasters’ Studio [TPS] – Ray Ortega

Podcast File Format and Embedded Information

Before analysing the audio of the individual podcasts we’ll first look at the podcast files themselves, their formats and any meta data contained therein. The tools used for this analysis were MediaInfo and Mp3tag.

	PAM	SOP	TAP	TPS
Ref. Episode	#351	#402	#167	#082
File Type	MP3	MP3	MP3	MP3
Codec	MPEG 1 Layer III	MPEG 1 Layer III	MPEG 1 Layer III	MPEG 1 Layer III
Bit Rate	128 kbps	64 kbps	64 kbps	128 kbps
Bit Rate Type	Constant	Constant	Constant	Constant
Sample Rate	44.1 kHz	44.1 kHz	44.1 kHz	44.1 kHz
Duration	1:01:32	1:08:59	0:36:59	1:01:52
File Size	56.7 MB	31.6 MB	17.0 MB	56.7 MB
Mono/Stereo	Joint Stereo (MS)	Mono	Mono	Joint Stereo (MS)
Filename	PAM351-SharkTankb.mp3	sop402_ 033114.mp3	tap167.mp3	TPS082_ _Zoom_H6_and_ Crowdfunding_for_ Podcasters.mp3
ID3 Genre	Podcast	Podcast	Technology	Podcast
ID3 Year	–	2014	2014	2014
ID3 Track	–	402	167	–
ID3 Album	PodcastAnswerMan.com	The Morning Announcements	The Audacity to Podcast	The Podcasters’ Studio
ID3 Artist	Cliff Ravenscraft	David Jackson	Daniel J. Lewis | Noodle.mx Network	Ray Ortega
ID3 Title	On Air Signs – Shark Tank Podcast – And So Much More	Jordan Harbinger Left His Law Career to Do Podcasting Full Time	What is RSS? And why you MUST own yours – TAP167	TPS082: Zoom H6 and Crowdfunding for Podcasters
ID3 Comments	–	518 chars	533 chars	98 chars
ID3 Image Size	541 kB JPEG 1400 x 1400px Other	35 kB JPEG 300 x 300px Front Cover	169 kB JPEG 1400 x 1400px Other	95 kB JPEG 600 x 600px Other
Other ID3 Tags	–	–	COPYRIGHT, ENCODEDBY, PODCAST, PODCASTDESC, PODCASTID, PODCASTURL, WWW	COMMENT ITUNNORM, COMMENT ITUNPGAP, COMMENT ITUNSMPB, ENCODEDBY, COMPOSER UNSYNCEDLYRICS

So, what does all this tell us?

Well, despite many commonalities, even amongst the leading proponents of podcasting there are clearly differences of opinion as to what approaches to adopt. There is obviously no perfect way of doing things, but perhaps more variations on a theme.

Cliff and Ray have gone for higher bit rates and stereo files, which while undoubtedly giving higher audio quality mean file sizes are proportionally larger and take longer to download.

Cliff Ravenscraft uses the least number of descriptive ID3 tags in the MP3 files, choosing to ignore even some of the most common podcast ID3 tags such as the year and track or podcast episode number. Ray and Daniel certainly win for the most number of ID3 tags and David and Daniel excel in their large comment fields.

Podcast cover art is pretty important as this is what listeners see on their playback devices. All of the podcasts incorporate cover art, although David Jackson opted for the Front Cover album art tag instead of the “Other” tag, which technically makes most sense I think, but ultimately depends on how the plethora of MP3 players available support these tags.

Audio Analysis

Waveform View

A simple waveform view of the sample audio files using the Audacity audio editor can give us a few clues about each podcast’s audio, providing useful comparisons:

In Daniels’s podcast (TAP) it’s interesting to note that his audio clipped briefly, indicated by the vertical red line. This is generally considered undesirable as it manifests itself as audible distortion.

Daniel’s audio was much more dynamic however compared to the others which were clearly heavily compressed and limited, preventing their audio levels from exceeding predetermined thresholds. We’ll discuss the dynamic range of the respective podcasts in more detail later in this article.

Frequency Response

Different microphones and different voices all contribute to different frequency or spectral responses and in this respect I’m not entirely sure how much the following graphs can tell us, other then they’re pretty to look at:

Two interesting points to note though are that Cliff’s podcast has an extended low end (bass) and Ray’s podcast has a significantly extended top end (high end or treble) potentially making his podcast brighter sounding.

Dynamic Range and Loudness

Amongst the broadcast industry recent European (EBU R128) and International (ITU-R BS 1770-1) standards have been developed and adopted to measure and help control the perceived loudness levels of audio content within programmes.

These standards call for a programme loudness level of -23.0 LUFS (measured across the entire programme) with a permitted deviation of ±1.0 LU, where 1 LU is equivalent to 1 dB.

Programmes are also allowed a maximum permitted true peak level of -1.0 dBTP. True peak rather than sample peak is specified as inter-sample peaks can often exceed the maximum sample peaks, leading to digital distortion and clipping.

The following measurements were taken using the free EBU R128 and ITU-R BS 1770-1 compliant loudness analyser plugin (MLoudnessAnalyzer) from MeldaProduction used from within Cubase:

	PAM	SOP	TAP	TPS
Loudness	-12.1 LUFS	-16.3 LUFS	-21.8 LUFS	-13.7 LUFS
True Peak	-0.37 dBTP	-3.81 dBTP	0.01 dBTP	-1.78 dBTP
Peak	-0.62 dBFS	-4.43 dBFS	-0.00 dBFS	-2.42 dBFS
Loudness Range (LRA)	3.4 LU	2.4 LU	2.8 LU	3.2 LU
Peak to Loudness Ratio (PLR)	11.73 dB	12.19 dB	21.81 dB	11.92 dB

Loudness Analysis

From the above table we can see that Cliff Ravenscraft’s podcast is the loudest and Daniel J. Lewis’ is the quietest. In fact Cliff’’s podcast is twice as loud as Daniel’s, with a 9.7 dB difference; 10 dB is usually considered as a perceptual doubling in volume.

Although the EBU R128 standard calls for a -23 LUFS loudness level in the broadcast industry, recent studies have recommended a -16 LUFS level (7 LU louder) for mobile devices due to the noisier environments in which they are likely to be listened to. In this respect, David Jackson’s podcast is pretty much spot on, Daniel’s is too quiet and the others are too loud.

Avoid Clipping

Digital distortion and clipping should be avoided at all costs and in this respect Daniel’s been a naughty boy as he exceeded 0 dBTP. Looking at the previous audio waveforms above however, it appears that Daniel only clipped at one point (the vertical red line on the right hand side of his waveform image), so perhaps he’s only been a little bit naughty.

Everyone else has avoided clipping, although Cliff is sailing a little close to the wind according to the current standards.

Dynamic Range Analysis

Dynamic Range is not the same as Loudness! A podcast can be loud, but have little dynamic range.

The loudness ranges for the podcasts measured were fairly consistent yet on the low side, which is not at all surprising considering the programme material was essentially spoken word.

The peak-to-loudness ratio (maximum true-peak compared to the average loudness level) is a more representative indication of the programme’s dynamic range measured over the short term. Looking at these figures we can see that Daniel’s podcast is by far the most dynamic as is also borne out by looking at the waveform of his podcast compared to the others.

Conclusions

What can we actually infer from the above analysis?

Well, if you can listen to the podcasts quite happily, wherever you want and on whatever equipment you have, with no problems and you enjoy them, then it means absolutely nothing at all.

If however, you’re an audio or podcast nerd, then it might be more interesting.

For myself the ID3 tags are of little importance when I’m listening to a podcast. Absolute audio perfection isn’t that important either, but I do hate audio clipping particularly as it causes my particular MP3 player to drop out momentarily at each clipping point. So for this reason I think the EBU recommendation of a maximum audio level of -1.0 dBTP is quite important.

Secondly, I hate significant variations in volume levels between podcasts and as we’ve seen from these few examples volume levels can vary tremendously.

While loudness and dynamic range are certainly not the same thing, they are linked and in the case of Daniel’s audio it would have to lose some of its dynamic range in order to increase its overall perceived loudness. Conversely though Ray and Cliff’s podcasts’ loudness could be reduced a little whilst simultaneously gaining more dynamic range.

Recommendations

1. Ensure your podcasts never exceed -1.0 dBTP
2. Engineer your podcasts to meet the -16 LUFS ±1 LU loudness level
3. Don’t compress or limit your podcasts too much to retain dynamic range

If you’d like to read more about these new audio broadcast standards and how they relate to podcasting, then there are some excellent articles on the Auphonic blog.

For what it’s worth those are my thoughts; they may change with time as I learn more, but that’s where I am at the moment. What are your thoughts or experiences?