MP3 encoding

[flintstone mop]

Hello ALL
We know that there are limitations for the audio response for broadcast on shortwave radio.
Allan Weiner is trying to streamline his operations by asking programmers to email their material. This would be nice to avoid Express mail charges for me. I'm guessing he'll program all of these email files into some sort of "player" and walk away for the next several hours and ball park the levels on the audio console, hoping for the station processing to catch the extremes in audio levels.
He is asking to reduce the size of a 60 minute program of typically 600mb down to 40mb. The loss of extreme audio would not be noticed on the air. BUT I do want to avoid low bitrates that give music or voice that watery sound.
What bitrate would get me close to the requested file size and maintain the best fidelity?
Should I ask what "player" they will use at the station? Or does it make any difference?
Thanks for any guidance


Fred

[Blaine N1GTU]

60 minute program of typically 600mb

its 10MB a minute for uncompressed stereo audio, you can cut that in half by mixing it down to mono (one channel).
this will get you down to 300MB
you can probably get away with encoding at 64k if you roll of the highs before encoding to avoid the aliasing.
would probably never hear the difference over shortwave AM
if not try 128k.
would probably get the program down to 20MB or less in filesize.
keep the original stereo recording uncompressed for archiving...

[W1RC]

Hi Fred:

I used to send THE REAL AMATEUR RADIO SHOW as an e-mail attachment up to Al in the late 'Nineties and early 2000s in .mp3 format.  I used mono (as Blaine pointed out it cuts the file size in half), 22,050 Hz @ 64 Kb/sec.  The programming was only voice frequencies and I could have made the file size even smaller.

Al likely uses WINAMP or some other .mp3 player program.

73 and good luck with the show.

MisterMike, W1RC

[flintstone mop]

Well, that's interesting news about recording in mono. Never thought of that and could have saved a lot of disc space. The music is turned into mono before the computer any way. I'll have to select to "record in mono" on the cooledit.

Archiving is only for replay when I'm outta time or during the no propagation weeks during the Winter. I have about 3 years of Flintstones in .WAV for editing and then it's just a quick step now to prepare to send over the 'Net.

I know about the aliasing at the slower bitrates. The high freqs get that watery sloshy sound. You know, even with those negatives, no one would ever notice with most listeners using those little hand held SW radios. But I want every bang I can get a hold of to go into the ether.

I have been rolling the highs (-8dB starting at 8kc and kill it completely (-20dB) above that) for the last month and the program seems louder. The processing seems to be peaking audio in the upper ranges somewhere near 4-5kc to get a little brighter audio for the programmers who send cassette type audio. But when my hi-fi music hits the processors, the distorion from all of the limiting and the reduced modulation takes all the fun out of listening. I know that Tim has brick wall filters for 5kc and there must be a lot of ringing from the high levels from the board. Timmy says he has walked in and seen the meters buried and that's when the processors take over and grunge it up more. That's called the bozo effect for the board ops.

Thanks for some valuable info Blaine and Mr Mike

Fred

[Steve - WB3HUZ]

A 40 MB MP3 file would be approximately 43 minutes. Details like whether it's VBR or not are not given but you can play some games with the calculator at the link below.

http://waxy.org/projects/mp3calc/

Here's another good chart that get you in the ballpark on how much compression occurs at the various bit rates.

Format     Bit rate   Compression ratio   File size per minute
WAV      uncompressed        1:1                   10 MB   
MP3        160 kbps          9:1                   1.5 MB   
MP3        128 kbps         11:1                   1 MB
MP3         96 kbps         15:1                   700K
MP3         64 kbps         22:1                   400K

[Opcom]

videolan is a free streamer and player. I have not used it for MP3 personally but in the ADSL lab we used it to stream videos over DSL.

[KA1ZGC]

Since WBCQ's brickwalled at 5 kHz, you shouldn't have any degradation that survives that filter from 22kHz-rate audio. You should have no problems packing that mofo right down.

[flintstone mop]

I'm gonna run with 96kbs MP3. The quality is very good and the total size is right where Allan wants a typical program at 40.1megs for a 1hr show. With WBCQ's brightness control, it will boost slightly, where I have attenuated and not be limited.
I'm still amazed at the relatively good audio that comes over the air with that bandwidth. It certainly sounds better than the local A.M.'s on both of my car radios.
I know it's an auto radio design flaw to filter out the IBOC crap. The stations that play music sound very nice on my R390A.
Thanks

Fred

[KA1ZGC]

I'm still amazed at the relatively good audio that comes over the air with that bandwidth. It certainly sounds better than the local A.M.'s on both of my car radios.

You can do a lot with a little if you care about the right properties.

The 7.415 transmitter is a pulse-width modulated Gates 50S (a close cousin to the Harris MW-50). It may be brickwalled at 5 kHz, but the transmitter itself imposes no audio limitations. The processing is utilizing every cycle from DC to 5 kHz. You may not get ultra-crisp cymbal crashes, but you still get very clean, robust, and pleasant audio.

Some PWM AM BC stations sound like crap because they're using the mentality of yester-decade, where the low-end response was to be brickwalled at 200 Hz because the mod iron usually couldn't pass it cleanly, and many receivers couldn't reproduce it anyway. It's not that way anymore, but many engineers were told as young JNs that "anything below 200 Hz is wasted energy" and just took that as Physical Law without ever asking "why".

A great example was WLBZ(/WACZ/WZON whatever they were at the time) 620 in Bangor. They went AM Stereo with a music format back in the late 80's trying to keep AM music alive. Had a great signal, great stereo image, good choice of tunes, but the audio sounded horrid. It was like listening to a cheap monaural hissette player with K-Tel-quality tape. They were on a pulse-width modulated transmitter, but it didn't matter, because Howie (the engineer) steadfastly refused to at least bring the low-end cutoff even down to 100 Hz or so. He was also over-protective of the high end, so the station was just plain narrow.

Now WZON's a mono sports-talk station, where those settings (still in effect today) don't do as much harm. Still audibly brickwalled at 200 Hz. Too bad, because he's wasting a perfectly good transmitter (even in a talk format), but it's his baby, not mine.

...but I digress.

Anyway, you should sound fantastic on 96k MP3, Phred.

[flintstone mop]

Yea Tom,
'BCQ's waveform is kinda neat to watch on the Oscope. I have one connected to the I.F. of my R390A. It's not a calibrated setup but a very nice display of MAX munkey schwangin.
I thought Timmy modded an MW-50 for 7415 shortwave. It's a one-of-a-kind TX.
You're right about the freq response, he said the limiting factor to modulated audio was the audio console.
I don't know if an Orban shortwave processor (it might restrict audio response too much!!!) would make anything better. It's about as loud as it can be. Many listeners email saying that the signal is BOOMING into their radios. Some folks have an audio amp and bigger speakers hooked up for the BIG sound.

Fred

[W1DAN]

Hi Fred:

Your MP3 settings should do fine. Your settings will give 12kc of audio.

As per ITU regulations, all shortwave stations audio must be gone by 5kc to fit in a 10kc channel. The big boys (VOA, BBC, etc) use an Optimod (9105a or 9400 today) processor that has the lows reduced (brickwalled at 50hz, but total energy below 200hz reduced) and a brick wall low pass filer at 4.5kc (24db/octave or even higher).

I dunno what WBCQ has for a low pass filter in their chain's processor. I thought they were running an Optimod 9000 or Inovonics 222, both of which have a higher low pass filter cutoff frequency. Maybe Timmy added a 4.5kc filter?

Either way the highs usually do not get to the listener's speaker as even their receivers dip pretty fast after 2kc or so.

73,
Dan
W1DAN

[KA1ZGC]

Tried to post this earlier, but my internet connection is spotty today...

I thought Timmy modded an MW-50 for 7415 shortwave.

I hear that a lot. I think I know why. I've seen that transmitter inside and out, it's a Gates 50S.

Having said that, there is not much difference between a Gates 50S and a Harris MW-50 (besides being the same company). Mostly the same transmitter with a slightly different cabinet(s) and tank circuit.

Tim probably refers to it as an MW-50 because the Gates 50S is not as well known, and it's close enough to an MW-50 that you still get pretty much the right idea if you imagine one in its place. The nameplate is different, the transmitter's abilities and basic construction are pretty much the same.

I don't know if an Orban shortwave processor (it might restrict audio response too much!!!) would make anything better. It's about as loud as it can be. Many listeners email saying that the signal is BOOMING into their radios. Some folks have an audio amp and bigger speakers hooked up for the BIG sound.

That pretty much nails it on the head. People get all up in arms about "you don't need all that bass", but whatever bass is in the program should damn well be there in the broadcast. That's my personal standard. That's a question of fidelity, not shaking the house to pieces, in my view.

I used to love Harv's closing music (yeah, we're going way back, here) because it really showed off the robust low-end of 7415. Plenty of other programs do, too, but Harv was quite a regular fixture on BCQ back then.

Never really looked at the Orban HF line. A 9100 (or similar) can give any AM signal whatever it needs, irrespective of frequency. I'm sure it's all (the HF line, that is) sold overseas, anyway: there are fewer licensed shortwave stations in this country than there are states.

Haven't been to Monticello in a few years, but I think there's a 9100 in the 7.415 chain. I know the 9.3xx chain (particularly the exciter) is mostly Pete SOV's brainchild. The other two have been modified too many times since my last visit to even guess.

[flintstone mop]

Hi Dan
I don't know what processing they're using either. Maybe Timmy told me CRL. I hope Allan stays away from the Orban shortwave processing. That would kill all the musical quality for 'BCQ.
Side Note: Very nice Russian station on 7125 Big low end.
This has been great reading and Tom, thanks. Give me a sig report if you have time to listen on Sundays 5-6P. We could PM any ideas about audio. I could explain what I'm doing with my processing.
THanks

Fred