user6099: Lately, my friends have been prompting me to buy an external audio recorder. They said that the quality of the sound is way better. I have always been using the internal audio recorder of my DSLR.
As for the gears, I own a prosumer Nikon DSLR and a 20 cm shotgun microphone with an XLR output. I don't think syncing would be a problem for me. I am thinking of the Zoom H4n as recommended by my friends. Is the audio quality of the audio that different? 

user8027: Getting the audio recording separated from the video recording is one of the best things you can do to improve your sound. What makes good camera placement doesn't always make for good audio placement. Also, your audio recorder can keep running while your camera isn't, so you don't miss anything.
That being said however, the zoom h4n has some mediocre pre-amps, you start to hear a hiss once you set the volume past 60 or so.

user2836: I wouldn't recommend the h4n anymore.  It is still a huge step up from the on-board audio, but it generally isn't the best value anymore.  The H5n or H6n are both better options available now and generally better value unless you are getting a used H4n that someone is selling so they can buy the 5n or 6n.
That said, yes, you want an external audio recorder.  The "internal audio recorder" on your camera is nothing more than a consumer level audio jack with a minimal quality capture capability.  It lacks key features like phantom power and balanced audio as well as lacking a high quality audio interface.  Monitoring is limited, the audio is heavily compressed and the connection is not secure and has to be plugged in to your camera.
An external recorder, such as something in the Zoom H#n series or higher end devices with similar function provides much cleaner audio as well as the ability to work with a much wider variety of high quality microphones.  Additionally, you can still use the output from the external recorder and feed it in to your mic input on the DSLR if you want to have audio on your rough footage (though I still recommend using the actual audio files from the recorder for your final audio.)  You don't need to have it connected to your camera if your camera needs to be moving.  It can be operated by a separate sound engineer without bothering the camera operator.  It is just all around a smoother and much higher quality experience.

user1950: Apart from the other benefits mentioned - mic placement, quality of the pre-amps, ability to properly monitor levels, another advantage is that many of the good quality digital recorders (like the Zooms) will let you record 24 bit samples at up to 96kHz. To use a not completely accurate analogy, that's like recording raw video at 4K instead of 8-bit at 1080p.

user4426: Can't speak for the Nikon, but the Canon 5D and 7D both have terrible on-board audio, with no way to easily monitor the audio levels.  The Zoom will have a better mic pre-amp, and will let you monitor the levels easily and accurately.  You can also monitor the audio on headphones whilst filming, so you'll stand a better chance of spotting problems, like wind noise, obtrusive background sounds, etc.

user5764: Yes, its way better. Being able to monitor the levels, and headphones, makes a huge difference.
However, its not even just the quality of the mic or recording device its the location. Having an external recorder means you can separate the audio easily from the camera. Back in the day when I was a teen, and had more enthusiasm than money, we used mics from old telephones to capture the actors speak. It improved our recording quality immensely, granted we also had a sound boom and sound operators, even so having the mic there on person saved our sounds more than once. Point is even a lousy mic in a great location is better than a great mic in a lousy location. 
So look at it this way now you have 2 sound sources.

user6671: There are a variety of reasons to have an external recorder depending on the size of your production.  A big advantage is the number of audio inputs and the ability to record each of those inputs as separate tracks, allowing you to do the mixing in post.  I'm not sure about the H4n, but I know the H5 and H6 support multiple inputs as well as interchangeable capsules.
Another advantage is quality and control over quality.  Most audio devices have a switch for uncompressed .WAV or compressed .MP3.  You always want uncompressed audio unless you are tight on space.  External audio devices also give you better control over gain and have better support for audio monitoring.
The final advantage I'll list here is portability.  When your mic is tied to your camera, you'll need to string cables from the mic to the camera.  This isn't an issue when the mic is sitting on the camera, but if you want a distance shot this becomes a problem.  External audio gives you much more freedom of movement to place your mic in the best position to pick up sound.

6099: <p>Lately, my friends have been prompting me to buy an external audio recorder. They said that the quality of the sound is way better. I have always been using the internal audio recorder of my DSLR.</p>

<p>As for the gears, I own a prosumer Nikon DSLR and a 20 cm shotgun microphone with an XLR output. I don't think syncing would be a problem for me. I am thinking of the Zoom H4n as recommended by my friends. Is the audio quality of the audio that different? </p>
 8027: <p>Getting the audio recording separated from the video recording is one of the best things you can do to improve your sound. What makes good camera placement doesn't always make for good audio placement. Also, your audio recorder can keep running while your camera isn't, so you don't miss anything.</p>

<p>That being said however, the zoom h4n has some mediocre pre-amps, you start to hear a hiss once you set the volume past 60 or so.</p>
 2836: <p>I wouldn't recommend the h4n anymore.  It is still a huge step up from the on-board audio, but it generally isn't the best value anymore.  The H5n or H6n are both better options available now and generally better value unless you are getting a used H4n that someone is selling so they can buy the 5n or 6n.</p>

<p>That said, yes, you want an external audio recorder.  The "internal audio recorder" on your camera is nothing more than a consumer level audio jack with a minimal quality capture capability.  It lacks key features like phantom power and balanced audio as well as lacking a high quality audio interface.  Monitoring is limited, the audio is heavily compressed and the connection is not secure and has to be plugged in to your camera.</p>

<p>An external recorder, such as something in the Zoom H#n series or higher end devices with similar function provides much cleaner audio as well as the ability to work with a much wider variety of high quality microphones.  Additionally, you can still use the output from the external recorder and feed it in to your mic input on the DSLR if you want to have audio on your rough footage (though I still recommend using the actual audio files from the recorder for your final audio.)  You don't need to have it connected to your camera if your camera needs to be moving.  It can be operated by a separate sound engineer without bothering the camera operator.  It is just all around a smoother and much higher quality experience.</p>
 1950: <p>Apart from the other benefits mentioned - mic placement, quality of the pre-amps, ability to properly monitor levels, another advantage is that many of the good quality digital recorders (like the Zooms) will let you record 24 bit samples at up to 96kHz. To use a not completely accurate analogy, that's like recording raw video at 4K instead of 8-bit at 1080p.</p>
 4426: <p>Can't speak for the Nikon, but the Canon 5D and 7D both have terrible on-board audio, with no way to easily monitor the audio levels.  The Zoom will have a better mic pre-amp, and will let you monitor the levels easily and accurately.  You can also monitor the audio on headphones whilst filming, so you'll stand a better chance of spotting problems, like wind noise, obtrusive background sounds, etc.</p>
 5764: <p>Yes, its way better. Being able to monitor the levels, and headphones, makes a huge difference.</p>

<p>However, its not even just the quality of the mic or recording device its the location. Having an external recorder means you can separate the audio easily from the camera. Back in the day when I was a teen, and had more enthusiasm than money, we used mics from old telephones to capture the actors speak. It improved our recording quality immensely, granted we also had a sound boom and sound operators, even so having the mic there on person saved our sounds more than once. Point is even a lousy mic in a great location is better than a great mic in a lousy location. </p>

<p>So look at it this way now you have 2 sound sources.</p>
 6671: <p>There are a variety of reasons to have an external recorder depending on the size of your production.  A big advantage is the number of audio inputs and the ability to record each of those inputs as separate tracks, allowing you to do the mixing in post.  I'm not sure about the H4n, but I know the H5 and H6 support multiple inputs as well as interchangeable capsules.</p>

<p>Another advantage is quality and control over quality.  Most audio devices have a switch for uncompressed .WAV or compressed .MP3.  You always want uncompressed audio unless you are tight on space.  External audio devices also give you better control over gain and have better support for audio monitoring.</p>

<p>The final advantage I'll list here is portability.  When your mic is tied to your camera, you'll need to string cables from the mic to the camera.  This isn't an issue when the mic is sitting on the camera, but if you want a distance shot this becomes a problem.  External audio gives you much more freedom of movement to place your mic in the best position to pick up sound.</p>
