Compressor on Radio Station

[DSA]

Hi,

 

I'm afraid its another Radio Question...but Compressors are pretty generic, so I am hoping that someone can help!

 

Last week I had a bit of a fiddle with our compressor (its the last link in the audio chain before going to the internet streamer and speakers around the building) to try and raise the level of the internet output. Clearly I had too much of a fiddle as it is now rather loud. I am just asking whether or not I have set it up correctly, and how to sort it out if I have!

 

Now it may be my ears, but I also think that I can hear a 'pumping' effect of the output, presumably as the compression takes place. Also voices sound wrong...by that I mean the s's seem to be accentuated etc.

 

Our compressor has 5 knobs...threshold, compression ratio, attack, release, and a gain knob at the end. I am more concerned that something is 'wrong' as currently I have the threshold at its lowest setting, and the ratio at its highest. That was the only way I could stop the sound distorting; as soon as I raise the threshold up a bit, the highs get distored.

 

I don't really know what to do with the attack/release - I think they are set somewhere in the middle at the moment.

 

It's annoying, because I made it sound great through the Production Studio Computer...and then got home onto my laptop and realised that it was far too loud.

 

On the main broadcast mixer, CD players, mics etc. are set to 0db at the desk (via gain pots) so the level should be fine coming into the compressor.

 

I hope someone can give me some pointers as to what the setting should be for a great and high enough level sound.

 

David

 

P.S. If you would like to listen to the stream here is a direct link: here. At the moment our sustainer is playing (Non stop play) - that level always was quieter than our output, so when that is on it is not really a true reflection of the stations output (although it still goes through the Compressor).

 

P.P.S. I have looked on google, and found some pointers, but they tend to be more directed at the recording/live sector and I am not too sure exactly where I have gone wrong, so any help would be most appreciated.

[James]

david.

 

You don't say exactly what the compressor is for. Typically in a radio studio you need to have a compressor immediately before the transmitter to address the risk of overmodulating the transmitter. This is less of an issue in the case of an internet "radio" station. (you are unlikely to have the police knock on your door for overmodulation - you just won't get any listeners as it sounds crap....)

 

You also don't say what type of programme content you produce. Obviously there is much higher dynamic range in live talk programming or classical music than in contemporary produced pop.

 

From what you say it sounds like you have you gain stage completely screwed and you are using the compressor as an attenuator - now if there wasn't a problem before you are a little screwed.

 

This is what I would do if you need a compressor

 

1) feed tone into your desk, check input gain and line up so you have 0dBu out of the desk.

2) bypass the compressor, (threshold +20, ratio 1:1, gain 0)

3) check the level passing into your transmission network.

 

once you have checked that there is nothing funny going on with your levels into the transmission network, I would experiment with the compressor trying a ratio of something between 2:1 and 3:1 starting with a soft knee at PPM4 or 0dBu I wouldn't put any gain on this.

 

if this if for protection then you want the attack fast, if it is for musicality then you want is slow. same with the release.

 

I would also consider getting a brick wall limiter set up at PPM6 (+8 dBu)

 

(If your compressor doesn't have a limiter then you can simulate it with threshold +8, ratio infinite, hard knee, no gain, and the fastest attack setting)

 

Good Luck and let us know how you got on.

 

James

[DSA]

I believe that the compressor was added (many years back) to ensure a consistent output level of the station, and to reduce distortion and clipping. It needs to be set right, as soon we are moving on to AM, and the signal will be sent to the transmitter via the Internet....(and therefore the compressor too).

 

Our output varies widely, from talk show style shows with added music during the day, to dance style 'specialist' shows at night. We definately want a clear sound.

 

You say feed tone to line up 0dBu. Our setup is so 'simple' that it is just 2 CD players, computer, and 3 mics each on their own channels. Operators are told to check that the level is at 0dbU before each link, so I would hope that the input to the compressor is near enough at 0dBu. I can certainly try out a tone, but I don't think that is where the problem lies.

 

What is the best way to check the level passing to the transmission network? Should I take my laptop down the studios? When I used the desktop I clearly got odd results (I am convinced because of the Spirit Desk in which the metering is messed up). Equally, what is a good (free) program to use to produce the tone?

 

Also, what does PPM mean?

 

Thanks for this help,

David

[James]

David.

 

If you are going AM in the future then you will need a brick wall limiter. Overmodulation is a very bad idea in broadcasting.

 

PPM meters are often used in broadcasting (Peak Programme Meters) They provide a nice easy way of seing what level output you are generating.

 

They differ from vu meters in scale,

 

http://plugin.org.uk/meterbridge/vu.png

 

Vu meters have a log scale, and show much quieter signals. They are usually marked in dB.

 

http://plugin.org.uk/meterbridge/ppm.png

 

PPM Meters do not have a dB marked scale, rather it shows 7 numbers evenly spaced. PPM markings are 4dB apart and ppm 4 equates to 0dBu

 

Many people find it is easier to explain to an operator that you are not allowed to go higher than PPM 6 and it should be louder than PPM 4 than to explain that on a non linear scale on a vu meter.

 

PPM units appear on ebay occasional this is one for example

 

James

[Bobbsy]

Ifyou want to use this as a chance to do some reading and actually teach yourself about compressors, I've always found the "Rane Notes" on the topic a very good resource. Although they're a manufacturer, the instructions can apply to any brand of compressor.

 

Have a look at: http://www.rane.com/pdf/note141.pdf

 

Hope it helps,

 

Bob

[DSA]

Right! Where do I start...(sorry for the 'story' style of the post, but I think it is the best way!)

 

I spent about 3 hours in the racks room this afternoon, and the result is a much better output! But it wasn't easy!

 

As there was a show in progress, I couldn't send a tone through at that moment, so instead I went to the compressor and set it as James said (first disconnecting the cafe downstairs!):

bypass the compressor, (threshold +20, ratio 1:1, gain 0)

the output was rediculously loud and distorted....something was seriously wrong. I double checked that the studio was giving out 0dBu (or thereabouts) and it was, and the sound sounded nice through the studio monitors...

 

So I turned the compressor back to where it was and had a good check of the signal path. After a few minutes I realised that I had forgotten the 'coffee machine'. (Its called that because of a sticker on the top...but thats another story!) It takes the feed from the compressor and splits it so that there is a feed to the cafe, the streamer, and the roof (for when we have RSLs for FM broadcast). Its a bit of a maze inside (looks like an A-level electronics project....), but sort of works. After fiddling around with various preset resistors and other connections in the box the stream level went very quiet - and I thought great!

 

Upon setting the compressor again as mentioned, the level was pretty good, if a little distorted in the highs. I quickly shut up the coffee machine before fiddling it back to how it was!

 

And then the stream went silent...somehow the streamer had turned off - I must have knocked a power cable or something, so I then had half an hour getting that back up...but thats another story.

 

Once the stream was back online I fiddled with the compressor settings for proper. I turned the attack and release to their lowest setting and ended up with the ratio at about 2.5, and the threshold at about -5. Adding a dash to the 'makeup' gain knob seemed to take the Winamp vu meter thing to about 0dBu in the loudest bits - yes I know that the winamp vu will be prettty useless, but its all I had at the time.

 

I reconnected the cafe, and went downstairs, and it was sounding better than ever - again the fiddle in the coffee machine must have sorted something there... However I am a little preturbed that the stream output is a little quiet now(!) What would be the best way to rise that without adding distortion?? (using the gain knob?) The additional volume in the cafe can be reduced with the knob on that separate amplifier.

 

I have received a kind offer of help with a tone source and meter. Will this be useful, or have I sorted it now? Again at the moment the sustainer is on...they are meant to be upping their level to meet ours, so as I said before it is not a true reflection of our output at the moment.

 

Thanks for the info re PPM James...the ebay one looks good, but how do I put it in the signal path, as there is only 1 set of XLRs on the back of the box? (surely it needs to go in and out, onto the coffee machine??)

 

Thanks again,

David

 

P.S. Thanks for the pdf link....I shall read that with interest tonight!

[Just Some Bloke]

I find the meters on the compressor, combined with my ears, a very useful way to set up a compressor.

 

Most compressors will have 2 sets of meters: one to show input and/or output levels, the other to show the amount of gain reduction. I would look at the levels coming in, listen to what needs compressing and then look at the input meter to see at what level the compression needs to kick in. Set that as your threshold setting. Then look to see how much gain reduction is going on above that threshold. If you can hear the pumping you mentioned earlier then your ratio setting is too high. Conversely, if it's not making enough difference, then your ratio setting is too low. If you fiddle about with the threshold and ratio settings within the guidlines I've just given you should soon be getting close to what you want. Check the input meter to see that the threshold is set correctly and the gain reduction meter to check the ratio is set correctly then listen to see how it sounds. Attack and release settings provide some 'fine tuning', and the output gain control lets you ensure that you're still sending the right level on to the rest of the system (it should be coming in at 0dB peak and going out at 0dB peak - that way you shouldn't be getting any distortion).

 

It's a matter of listening to how it sounds and using the meters as a visual guide to what's happening.

 

Hope that helps.

[DSA]

I find the meters on the compressor, combined with my ears, a very useful way to set up a compressor.

 

Most compressors will have 2 sets of meters: one to show input and/or output levels, the other to show the amount of gain reduction.  I would look at the levels coming in, listen to what needs compressing and then look at the input meter to see at what level the compression needs to kick in.  Set that as your threshold setting.  Then look to see how much gain reduction is going on above that threshold.  If you can hear the pumping you mentioned earlier then your ratio setting is too high.  Conversely, if it's not making enough difference, then your ratio setting is too low.  If you fiddle about with the threshold and ratio settings within the guidlines I've just given you should soon be getting close to what you want.  Check the input meter to see that the threshold is set correctly and the gain reduction meter to check the ratio is set correctly then listen to see how it sounds.  Attack and release settings provide some 'fine tuning', and the output gain control lets you ensure that you're still sending the right level on to the rest of the system (it should be coming in at 0dB peak and going out at 0dB peak - that way you shouldn't be getting any distortion).

 

It's a matter of listening to how it sounds and using the meters as a visual guide to what's happening.

 

Hope that helps.

<{POST_SNAPBACK}>

 

Unfortunately, our fairly cheepo compressor has only got a meter for gain reduction, and not input/output levels - so I guess I need to get hold of a meter, as James suggests.

 

David

 

EDIT: Is it worth getting a simple EQ to go in line with the compressor? Not only to improve the sound quality, but to reduce background noise eg. hissing which can be heard in the quiet passages. As the studio tends to sound very 'tinny', would some carpet help?

[david.elsbury]

What level is the compresser operating at? +4 or -10? Check that whatever you are using, it's the same as the output from the console or whatever. If you're getting a really hot and distorted signal, it could be at the wrong setting.

[IanG]

Is it worth getting a simple EQ to go in line with the compressor?  Not only to improve the sound quality, but to reduce background noise eg. hissing which can be heard in the quiet passages. 

<{POST_SNAPBACK}>

 

No. You've fallen into the "something is wrong, lets add more kit to fix it" solution, which invariably makes things worse. If you're getting hiss on your output when your broadcast chain is CD -> Desk -> Compressor -> Distribution Amp (coffee machine?) -> Output, then you have a problem. Get a pair of cans and listen to the outputs at various stages, and see what bit of kit introduces your hiss.

 

Then, fix or replace it. From what you've written so far, I'd suspect your DA (coffee machine) of being dodgy and would want to replace it. They're cheap enough to buy a fairly decent one off the shelf now.

 

Also, when you're doing an FM RSL, do you hire in a decent multiband compressor for that? In my experience most student stations do and it would be wise to have a pre-compressor feed to that.

[DSA]

Is it worth getting a simple EQ to go in line with the compressor?  Not only to improve the sound quality, but to reduce background noise eg. hissing which can be heard in the quiet passages. 

<{POST_SNAPBACK}>

 

No. You've fallen into the "something is wrong, lets add more kit to fix it" solution, which invariably makes things worse. If you're getting hiss on your output when your broadcast chain is CD -> Desk -> Compressor -> Distribution Amp (coffee machine?) -> Output, then you have a problem. Get a pair of cans and listen to the outputs at various stages, and see what bit of kit introduces your hiss.

 

Then, fix or replace it. From what you've written so far, I'd suspect your DA (coffee machine) of being dodgy and would want to replace it. They're cheap enough to buy a fairly decent one off the shelf now.

 

Also, when you're doing an FM RSL, do you hire in a decent multiband compressor for that? In my experience most student stations do and it would be wise to have a pre-compressor feed to that.

<{POST_SNAPBACK}>

Yes I suspect a dodgy DA too...after poking around inside! Its not very good, as the main output is on phono to the streamer and the cafe, as I believe the XLR output is broken... What would you recommend as a good, but fairly cheap one? (needs stereo input, and 4 (one spare) balanced stereo outputs (on XLR hopefully). Then I'll have to make up some stereo 3.5mm jack to 2 XLR cables...exciting!

 

We appear to have another problem though, in that the sustainer feed is at maximum, but is much lower than the desk feed. Clearly we want the two to be roughly the same, so do I need some sort of preamp in the sustainer feed (before the compressor - which compresses both the sustainer and the desk output, as there is a switch by the desk to switch between sustain and studio)??

 

Or is there a simpler (and cheaper) way of getting the two levels the same?

 

I still don't see how to put a PPM meter in, if it only has 1 XLR input per channel - does it need a mic splitter cable (ie 1 Female XLR to 2 Male XLR - 1 to the meter, and one to the compressor)??

 

I don't know about RSLs as we have saved money ready for AM, and not had one this year since I have been here, however I doubt that another compressor has been hired in.

 

This is all most helpful,

David

 

Edit: Or will RCA Phono connectors be OK? I am always a bit wary of them as they can easily pull out...

[ianl]

Yes I suspect a dodgy DA too...after poking around inside! Its not very good, as the main output is on phono to the streamer and the cafe, as I believe the XLR output is broken...  What would you recommend as a good, but fairly cheap one? (

 

 

http://www.behringer.com/MX882/index.cfm?lang=ENG

[IanG]

What would you recommend as a good, but fairly cheap one? (needs stereo input, and 4 (one spare) balanced stereo outputs (on XLR hopefully).  Then I'll have to make up some stereo 3.5mm jack to 2 XLR cables...exciting!

We had a Behringer one when I was in student radio, and that did a perfectly good job. Link in ianl's post.

 

We appear to have another problem though, in that the sustainer feed is at maximum, but is much lower than the desk feed. 

 

What is your sustainer? A DSat box? Is it balanced or unbalanced.

 

Or is there a simpler (and cheaper) way of getting the two levels the same?

 

Run it into a channel input on your desk, use that to match levels.

 

I still don't see how to put a PPM meter in, if it only has 1 XLR input per channel - does it need a mic splitter cable (ie 1 Female XLR to 2 Male XLR - 1 to the meter, and one to the compressor)??

 

No, you'll need to feed it from a DA, and (importantly) on an output which has been calibrated with known tone. Splitter cables work, but aren't ideal when used in accurate monitoring environments.

 

I don't know about RSLs as we have saved money ready for AM, and not had one this year since I have been here, however I doubt that another compressor has been hired in.

 

Okay - although I'd hope some limiting was included to prevent overmod. I've seen many transmitter 'packages' from hire companies including some kind of processor - in our case it was an Omnia I think.

[DSA]

What is your sustainer? A DSat box? Is it balanced or unbalanced.

No...its quite complicated I'm afraid. Our sustainer is basically just another internet radio station. They have provided a PC (therefore stereo 3.5mm jack output) which is constantly connected to their stream. This PC is located in the racks room about 20m away from the main studio. via 2 XLR cables (balanced) the sustainer feed goes into a balanced switch box. The output from the broadcast desk goes to the other side of the switch. The return feed from the switch then goes back via 2 XLR cables back to the racks room and into the compressor etc. which is in there.

 

The sustaining company (who made the switch) have also provided a direct feed from the switch box for a fader on the desk, but this is not connected up as we have run out of channels.

 

The idea behind the switch is to make it REALLY easy for presenters to switch over to the sustaining service at the end of shows. We used to do it ourselves via a playlist on winamp, but very often it would be forgotten and would result in silent output out of hours, which was far from ideal.

 

The switch works very well, and DJs no longer seem to forget, but as I say there is an inbalance in the output levels, and as you can hear the sustainer is quite low level.

Or is there a simpler (and cheaper) way of getting the two levels the same?

Run it into a channel input on your desk, use that to match levels.

As I said above, this is not really an option as we have no spare channels and it would be complicated for DJs (we have just got them used to this....these Arts student find it hard with all this technology you see (!)

I still don't see how to put a PPM meter in, if it only has 1 XLR input per channel - does it need a mic splitter cable (ie 1 Female XLR to 2 Male XLR - 1 to the meter, and one to the compressor)??

No, you'll need to feed it from a DA, and (importantly) on an output which has been calibrated with known tone. Splitter cables work, but aren't ideal when used in accurate monitoring environments.

Does the meter need to be in front of the DJs, or will it be OK in the racks room?....as I say above, it would require quite a bit of extra cabling if it needs to be in the studio. Or is there another way?

I don't know about RSLs as we have saved money ready for AM, and not had one this year since I have been here, however I doubt that another compressor has been hired in.

Okay - although I'd hope some limiting was included to prevent overmod. I've seen many transmitter 'packages' from hire companies including some kind of processor - in our case it was an Omnia I think.

No doubt there was the right kit in place, there is a chap who deals with all the RSLs etc. and I am sure that he would have put in /will put in what was/is necessary.

 

David

 

Goodness knows what is going on with these quotes. I can't get it to work!

 

Edit: Sorted now! (but something funny was going on!)

[IanG]

Our sustainer is basically just another internet radio station.  They have provided a PC (therefore stereo 3.5mm jack output) which is constantly connected to their stream.  This PC is located in the racks room about 20m away from the main studio.  via 2 XLR cables (balanced) the sustainer feed goes into a balanced switch box. 

 

Ah. So essentially you're going from a 3.5mm jack on the PC to 2 XLR cables? That won't be balanced (which might account for some of the hiss, and a 6dB loss in gain over a proper balanced circuit.)

 

The fact you're coming from a PC sound card might also explain the lower level - it certainly won't be outputting pro level signals.

 

It might be worth you getting something like an Alice Promatch or a Sonifex RB-UL1 (or a cheaper equivalent which I cant think of right now) to balance the run and sort out the levels. (Even an el-cheapo mixer would do).

 

 

Does the meter need to be in front of the DJs, or will it be OK in the racks room?....as I say above, it would require quite a bit of extra cabling if it needs to be in the studio.  Or is there another way?

 

 

Depends on what you want - Presenters certainly need to see a PPM to line up their levels correctly, but then it's also useful to have one in the engineering areas to ensure gain structure is set up correctly.