November 2013
M T W T F S S
« Oct   Dec »
 123
45678910
11121314151617
18192021222324
252627282930  

Archives

Categories

Meanwhile, at the helpdesk

If you have not seen this Youtube video, put down the coffee (or whatever) and move any spill able things away from the keyboard and enjoy:

What bitrate is needed to sound like analog FM?

As it turns out, 300 kbp/s or greater.  At least in critical listening environments according to the paper titled Perceived Audio Quality of Realistic FM and DAB+ Radio Broadcasting Systems (.pdf) published by the Journal of the Audio Engineering Society. This work was done by group in Sweden and made various observations with different program material and listening subjects. Each person was given a sample of analog FM audio to listen to, then they listened to various audio selections which were using bit reduction algorithms (AKA CODEC or Compression) and graded each one.  The methodology is very thorough and there is little left for subjective interpretation.

In less critical listening environments, bit rates of 160-192 kbp/s will work.

I made a chart and added HD Radio’s proprietary CODEC HDC, which is similar to, but not compatible with AAC:

System Codec Bit Rate (kbp/s)
HD Radio FM; HD1 channel* HDC (similar to AAC) 96 – 144
HD Radio FM; HD2 channel* HDC 24-48
HD Radio FM; HD3 channel* HDC 24-48
HD Radio AM* HDC 20-60
DRM30 (MF-HF) AAC/HE-AAC 34-72
DRM+ (VHF) AAC/HE-AAC 700
DAB+ AAC/HE-AAC 32 – 128
DAB MPEG II, Dolby digital 192 – 256
Blu-ray PCM** ≥6 Mbp/s
DVD PCM, DTS, Dolby digital >800
CD-A PCM 1,411
Web Streaming MPEG I,II,III, WMA, AAC, etc 32-320, 128 typical
iTunes AAC 128 – 256
Spotify Ogg Vorbis 96 – 320
Wimp AAC/HE-AAC 64 – 256

*Hydbrid mode
**PCM: uncompressed data

This is the composite Mean Basic Audio Quality and 95% confidence intervals for system across all excerpts:

digital-analog-audio-compar

Over the years, we have simply become accustomed to and now accept low quality audio from mp3 files being played over cheap computer speakers or through cheap ear buds.  Does this make it right?  In our drive to take something good and make it better, perhaps it should be, you know: Better.

Special thanks to Trevor from Surrey Electronics Limited.

A few updates

UPDATE: I notice that Radio World has a little star rating system on their articles. According to the rating, twenty one people think I suck… That is okay, but when I started looking around at all of the other articles on the website, I noticed most have but one or two votes.  It seems odd to me that my little opinion piece would have so many negative votes, especially in light of the e-mails, phone calls and personal interactions I have received supporting my position. 

Perhaps a few of you could run over there, read the article then objectively decide what you think… Here is the link: AM Efforts Should Include Tech Solutions

I am deeply immersed in all things networking, yet again. I regret the sparse posts, but there are a few things of note:

  1. It appears the the WYFR shortwave site in Okeechobee has been sold to the operators of WRMI (Radio Miami International).  This is a good turn of events for shortwave broadcasting.  WRMI programmed mostly to the Caribbean and were difficult to hear in these parts.
  2. Nielsen Radio, formerly Arbitron, says it will increase the sample size for the PPM program.  This is good, larger sample size means better accuracy and fewer extrapolation related errors and strange rating spikes.
  3. I published an commentary in Radio World Commentary: AM Efforts Should Include Tech Solutions. What do you think? Should the industry be looking at something other than HD Radio?
  4. Then, from across the pond there is this:

    Which is a digital radio promotion from the BBC. It seems Great Brittan is trying to force an all digital transition. A glimpse of things to come?

  5. In spite of the lack of posts, the blog continues to grow, averaging 550 to 600 page views per day with about 180 RSS subscribers.  As far as content goes, I can assume more of the same will suffice.

As time becomes available, I will post more.

Analog Sauce

A little blast from the past. This was found in a transmitter manual at one of the sites we take care of:

CCA Optomod 8000

CCA Optomod 8000

I thought I would scan it and make it available here.  As luck would have it, there is also a corresponding piece of equipment to go along with it.  I had never seen a “CCA Optomod” (.pdf) before I was working at one of the radio stations in Trenton, Florida.  This unit was rescued from under a pile of garbage out in the lawn shed.  It was full of mud was nests and mouse droppings.  Needless to say, it required a bit of TLC to return it to operation.  I replaced the electrolytics, cleaned it up and ran some audio through it.  It is probably as good as the day it left the factory.  Bob Orban made some really good stuff in his day.

CCA Optomod 8000

CCA Optomod 8000

The original Optomod 8000 was an evolutionary design that made FM radio processing what it is today.  The idea of combining broadband limiter, AGC and stereo generator in one box was a radical departure from the norm.  The audio limiter functioned as a 15 KHz low pass filter and broadband AGC.

Orban Optomod 8000 audio limiter block diagram

Orban Optomod 8000 audio limiter block diagram

The stereo generator used very modest amounts of composite clipping to reduce overshoot and transients. Many people disparage composite clippers. If done correctly, it is transparent to the listener and increases perceived loudness by stripping off modulation product that is non-productive.

Orban Optomod 8000 Stereo Generator block diagram

Orban Optomod 8000 Stereo Generator block diagram

Some thirty five or so years later, there are still many of these units in service in various stations around the world.

Network Data Flow Analysis

PRTG network sun

PRTG network sun

As more and more broadcast facilities are moving toward IP data for all types of data transfer including digitized audio, video, telephony, documents, email, applications and programs.  Managing an IP network is becoming more and more important.  In most broadcast facilities, Ethernet based IP networks have been the normal operating infrastructure for email, printing, file sharing, common programs, file storage and other office functions for many years.  Either directly or indirectly, most broadcast engineers have some degree of experience with networking.

With many more IP based audio consoles, routing systems, STL’s and other equipment coming online, understanding IP networking is becoming a critical skill set.  Eventually, all distribution of content will transition to IP based systems and the current network of terrestrial broadcast transmitters will be switched off.

The difference between an ordinary office network and an AoIP (Audio over IP) or VoIP network is the transfer consistency.  In an office network, data transfer is generally bursty; somebody moves a file or requests an HTTP page, etc.  Data is transferred quickly from point A to point B, then the network goes back to its mostly quiescent state. In the AoIP environment, the data transfer is steady state and the data volume is high.  That is to say, once a session is started, it is expected to say active 24/7 for the foreseeable future. In this situation, any small error or design flaw, which may not be noticed on an office network can cause great problems on an AoIP network.  The absolute worst kind of problem is the intermittent failure.

Monitoring and analyzing data flow on a network can be a critical part of troubleshooting and network system administration.  Data flow analysis can discover and pinpoint problems such as:

  • Design flaws, infrastructure bottle necks and data choke points
  • Worms, viruses and other malware
  • Abusive or unauthorized use
  • Quality of Service (QoS) issues

Cisco defines flow as the following:

A unidirectional stream of packets between a given source and destination—both defined by a network-layer IP address and transport-layer source and destination port numbers. Specifically, a flow is identified as the combination of the following seven key fields:

  • Source IP address
  • Destination IP address
  • Source port number
  • Destination port number
  • Layer 3 protocol type
  • ToS byte
  • Input logical interface

Packet sniffers such as Wire Shark can do this, but there are far better and easier ways to look at data flow.  Network monitoring tools such as Paessler PRTG can give great insight as to what is going on with a network.  PRTG uses SNMP (Simple Network Management Protocol) on a host machine to run the server core and at least one other host to be used as a sensor.  There are instruction on how to run it as a virtual machine on a windows server, which would be the proper way to implement the server, in my opinion.

For small to medium installations, the freeware version may be all that is needed.  For larger network and major market installation, one of the lower cost paid versions may be required.

Exploding Parts

We or rather, I have been working on installing this CCA transmitter as a backup unit at one of our sites. It was installed as a backup at another site, but was mothballed about ten years ago. Now, we need to get it running again and re-tune it. Seems like a fairly uncomplicated job.

CCA FM-5000DS transmitter, circa 1971

CCA FM-5000DS transmitter, circa 1971

Except, every time I start it, another one of these 1000 pf bypass/feed through capacitors fails. They are located at various points around the PA enclosure and route AC voltages into and out of that enclosure.  The bypass function is needed to keep stray RF off of the control circuits. Normally, they have been failing with a medium resistance fault (40-70 ohms) to case.  That causes the control circuit breaker to trip.

This time, however, it was on the primary for the filament transformer on the IPA tube.  Just a wee little pop, followed by some ozone smell and sans power output.  I have, thus far replace four of these and there are seven original still in the transmitter.

Feedthru capacitors

Feedthru capacitors

It is time to replace them all, otherwise this rig will fail when we need it the most.  Replacement part is a Mouser 800-24437X5S0102MLF, 1000 pf 500 v made by Tusonix Electronics.

Axiom


A pessimist sees the glass as half empty. An optimist sees the glass as half full. The engineer sees the glass as twice the size it needs to be.

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
~1st amendment to the United States Constitution

Any society that would give up a little liberty to gain a little security will deserve neither and lose both.
~Benjamin Franklin

The individual has always had to struggle to keep from being overwhelmed by the tribe. To be your own man is hard business. If you try it, you will be lonely often, and sometimes frightened. But no price is too high to pay for the privilege of owning yourself.
~Rudyard Kipling

Everyone has the right to freedom of opinion and expression; this right includes the freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers
~Universal Declaration Of Human Rights, Article 19

...radio was discovered, and not invented, and that these frequencies and principles were always in existence long before man was aware of them. Therefore, no one owns them. They are there as free as sunlight, which is a higher frequency form of the same energy.
~Alan Weiner

Free counters!