Troubleshooting Bad Sound

Troubleshooting Bad Sound

by Bruce Bartlett

Suppose you're monitoring a recording in progress, or you're listening to a recording you've already made. Something doesn't sound right. Maybe the bass is muddy, the cymbals are dull, the guitars sound too distant, and the vocal is distorted. Or maybe the whole mix is limp and lifeless.

How can you pinpoint what's wrong, and how can you fix it?

This guide offers some tips on solving problems with sound quality. Read down the list of "bad sound" descriptions until you find one matching what you hear. Then try the solutions until your problem disappears. Only the most common symptoms and cures are mentioned; console maintenance is not covered.

This troubleshooting guide is divided into four main sections:
1. Bad sound on all recordings (including those from other studios)
2. Bad sound on playback only (the mixer output sounds all right)
3. Bad sound in a pop-music recording
4. Bad sound in a classical-music recording

Before you start, check for faulty cables and connectors. Also check all control positions; rotate knobs and flip switches to clean the contacts; clean connectors with cleaning fluid such as De-Oxit from Caig Labs.

PART 1: BAD SOUND ON ALL RECORDINGS
If all the recordings you play sound bad, including those from other studios, follow this checklist to find the problem:
In general, upgrade your monitor system!

  • Adjust tweeter and woofer controls on speakers.
  • Adjust the relative gains of tweeter and woofer amplifiers in a bi-amped system.
  • Relocate speakers to change their frequency response. The closer speakers are to walls, the more bass the speakers have.
  • Improve room acoustics.
  • Equalize the monitor system.
  • Try different speakers.
  • Upgrade the power amp and speaker cables.

PART 2: BAD SOUND ON PLAYBACK ONLY
Maybe just the tape playback sounds bad, even though your mixer output sounds okay. If a cassette or open-reel tape plays back with a dull sound or drop-outs, follow these steps:

  • Check that the oxide side of the tape is against the heads.
  • Clean and demagnetize the tape path.
  • Try another brand of tape.
  • Align tape heads; calibrate the electronics.
  • Do maintenance on the tape transport.
  • Check and replace tape heads if necessary.
  • Don't record near the head or tail of the reel.
  • If the tape was recorded without Dolby noise reduction, be sure to switch off Dolby on your tape deck. Using Dolby will roll off the highs on tape that were recorded without Dolby.

If your tape playback is plagued with distortion, try the following:

  • Reduce the recording level.
  • Increase the bias level.
  • Check for bad cables.
  • If the recorder is digital, set the recording level to peak at 0 dB maximum.

If your tape playback has tape hiss, follow these steps:

  • Increase the recording level.
  • Use Dolby noise reduction during recording and playback.
  • Use better tape.
  • Align the tape recorder.
  • Try a faster recording speed.
  • Consider using a digital recorder instead of analog.

If DAT tape playback has glitches or drop-outs, try these steps:

  • Clean the recorder with a dry cleaning tape.
  • Before recording, fast-forward the tape to the end and rewind it to the top.
  • Use better tape.
  • Format videocassettes nonstop from start to finish.
  • Have the heads checked; they might be worn out.

PART 3: BAD SOUND IN A POP-MUSIC RECORDING SESSION
By "pop music" I mean anything that's not classical music. Pop music is generally recorded with multiple close-up microphones rather than with a stereo pair of mics. Suppose you're in a recording session, and the sound you're getting from the mixer is flawed. Find a description below that matches what you're hearing, and try the solutions listed.

MUDDY (EXCESSIVE LEAKAGE) If the sound is distant or muddy due to leakage between mics, try the following:

  • Place the microphones closer to their sound sources.
  • Spread the instruments farther apart to reduce the level of the leakage.
  • Place the instruments closer together to reduce the delay of the leakage.
  • Use directional microphones (such as cardioids).
  • Overdub the instruments.
  • Record the electric instruments direct.
  • Use baffles (goboes) between instruments.
  • Deaden the room acoustics (add absorptive material, flexible panels, or slot absorbers).
  • Filter out frequencies above and below the spectral range of each instrument. Be careful or you'll change the sound of the instrument.
  • Turn down the bass amp in the studio, or monitor the bass with headphones instead.

MUDDY (EXCESSIVE REVERBERATION)
If the sound is "washed out" and distant, there might be too much reverberation in the mix. Try these steps:

  • Completely turn down the effects-return levels. Listen to the mix. Is it clear now, or are there other problems, such as leakage? If the problem is leakage, try the solutions under that heading. If the sound is clear with reverb off, don't use so much reverb in the mix.
  • Try using reverb with a predelay of about 100 msec.

MUDDY (LACKS HIGHS)
Is the sound muddy because the high frequencies are weak? Does the mix have a dull or muffled sound? Try the following:

  • Use microphones with better high-frequency response, or use condenser mics instead of dynamics.
  • Change the mic placement. Put the mic in a spot where there are sufficient high frequencies. Keep the high-frequency sources (such as cymbals) on-axis to the microphones.
  • Use small-diameter microphones, which generally have a flatter response off-axis.
  • Boost the high-frequency equalization.
  • Change musical instruments; replace guitar strings; replace drum heads. (Ask the musicians first!)
  • When bouncing tracks on an analog recorder, record bright-sounding instruments last to reduce generation loss.
  • Avoid excessive recording levels with bright-sounding instruments. The high-frequency response of cassettes and open-reel tapes rolls off as the recording level is increased.
  • Use an enhancer signal processor, but watch out for noise.

MUDDY (LACKS CLARITY)
If your mix sounds unclear in general, try these steps:

  • Consider using fewer instruments in the musical arrangement.
  • Equalize instruments differently so that their spectra don't overlap.
  • Try less reverberation.
  • Using equalizers, boost the presence range of instruments that lack clarity.
  • In a reverb unit, add about 30 to 100 msec of predelay.
  • Try recording digital instead of analog.

DULL BASS GUITAR
If a bass guitar sounds murky, try these tips:

  • Use a direct box on the electric bass.
  • Have the bassist play percussively or use a pick if the music requires it.
  • When compressing the bass, use a long attack time to allow the note's attack to come through. (Some songs don't require sharp bass attacks--do whatever's right for the song.)
  • Boost EQ around 700 Hz to 2.5 kHz. *Use the treble pickup near the bridge.
  • Try a different bass guitar.

DULL KICK DRUM
The kick-drum sound you're getting might be flabby instead of punchy. These suggestions might help: *Listen to the live kick drum and make sure it sounds punchy. Maybe it needs a new head, a harder beater, or retuning.

  • Remove the front head and damp the kick drum with a pillow or blanket.
  • Mike the kick drum next to the center of the head near the beater.
  • Use a wooden beater if the song and the drummer allow it.
  • Boost EQ around 3 to 10 kHz.
  • Cut EQ around 400 to 600 Hz.

DISTORTION
If you have distortion in a pop-music recording, try the following:

  • Check connectors for stray wires and bad solder joints.
  • Unplug and plug-in connectors.
  • If the mic preamp is clipping, increase the input attenuation (reduce the input gain), or plug in a pad between the microphone and mic input.
  • If the mixer itself is distorting, readjust gain-staging: set faders and pots to their design centers (shaded areas).
  • If you still hear distortion, switch in the pad built into the microphone (if any).
  • If the mic is distorting and has no built-in pad, move the mic farther from the source or try another mic. Dynamic mics have almost no distortion.

To reduce digital distortion or graininess:

  • Record at 0 dBFS maximum.
  • Turn on dithering in a digital recording system.
  • Use as little digital processing as possible.
  • Use a digital recording system with more bits: 20 or 24 instead of 16.
  • Use digital gear that is current; much early digital equipment sounded bad.

BAD TONAL BALANCE
If the tone quality is unnatural -- boomy, colored, dull, or shrill, for example -- follow these steps: *Change musical instruments; change guitar strings; change reeds, etc.

  • Change mic placement. If the sound is too bassy with a directional microphone, you may be getting proximity effect. Mike farther away or roll off the excess bass.
  • Use the 3:1 rule of mic placement to avoid phase cancellations. When you mix two or more mics to the same channel, the distance between mics should be at least three times the mic-to-source distance.
  • Try another microphone. If a cardioid mic's proximity effect is causing a bass boost, try an omnidirectional mic instead.
  • If you must place a microphone near a hard reflective surface, try a boundary microphone on the surface to prevent phase cancellations.
  • Change the equalization. Avoid excessive boost.
  • Use equalizers with a broad bandwidth, rather than a narrow, peaked response.

MIXES DON'T TRANSLATE TO OTHER SPEAKERS
If your mixes sound good over your monitor speakers, but sound bad on other speakers, it's likely that your monitor speakers and room acoustics are not flat, or are not representative of real-world speakers. For example, if your monitor speakers are bright (too strong in the highs), your mixes will sound dull (weak in the highs) on many other speakers.

Solutions:

  • Listen to your mix on a variety of playback systems: on other studio monitors, in the car, on a boom box, etc. Make sure your mix sounds reasonably good on all of them.
  • Monitor at a moderate level, around 85 dB SPL. If you monitor at a higher level, the bass and upper midrange will be exaggerated, causing you to mix in not enough bass or upper mids.
  • Try a different model of monitor speakers and do a mix with them. See if your mix translates better to other speakers.
  • Equalize your monitor system with a graphic equalizer to provide a frequency response that translates well to other speakers. For example, if your mixes are too dull in the highs, roll off the highs in your monitors so that you will boost the highs to compensate. Then your mixes will sound brighter on other speakers.
  • Reposition your monitor speakers to change their frequency response.
  • Work on the room acoustics to change the frequency response.

LIFELESS
If your pop-music recording has a lifeless, unexciting sound, these steps might help you fix it:

  • Work on the live sound of the instruments in the studio to come up with unique effects.
  • Add special effects -- reverberation, echo, exciter, doubling, equalization, etc.
  • Use and combine recording equipment in unusual ways.
  • Try overdubbing little vocal licks or synthesized sound effects.

If your sound seems lifeless due to dry or dead acoustics, try these ideas:

  • If leakage is not a problem, put microphones far enough from instruments to pick up wall reflections. If you don't like the sound this produces, try the next suggestion.
  • Add reverb or echo to dry tracks. (Not all tracks require reverberation. Also, some songs may need very little reverberation so that they sound intimate.)
  • Use omnidirectional microphones.
  • Add hard reflective surfaces in the studio, or record in a hard-walled room.
  • Allow a little leakage between microphones. Put mics far enough from instruments to pick up off-mic sounds from other instruments. Don't overdo it, though, or the sound becomes muddy and track separation becomes poor.

NOISY (HISS)
Sometimes the signal from the mixer is noisy. If you hear hiss coming through the monitors, try these suggestions:

  • Maybe you're just listening at an unrealistically high level. Any mic signal has audible hiss if you listen to it very loudly.
  • Turn down the master faders and listen. If you still hear hiss, it is from the power amplifier. Either turn down the power-amp level or get a quieter amp.
  • Check mixer gain staging. The master and submaster faders should be at or near design center, the shaded portion of fader travel.
  • Reduce the mixer input attenuation (increase the input gain) up to a point about 10 dB below clipping.
  • Check for noisy guitar amps or keyboards. Turn up the guitar and turn down the guitar amp. Maybe replace bad tubes, or replace the amp.
  • Switch out the pad built into the microphone (if any).
  • Use a more sensitive microphone.
  • Use a quieter microphone (one with low self-noise).
  • Increase the sound pressure level at the microphone by miking closer. If you're using PZMs, mount them on a large surface or in a corner.
  • Apply any high-frequency boost during recording, rather than during mixdown.
  • If possible, feed tape tracks from mixer direct outs or insert sends instead of group or bus outputs. *Use a lowpass filter (high-cut filter).
  • As a last resort, use a noise gate.

NOISY (RUMBLE)
If the noise is a low-frequency rumble, follow these steps:

  • Reduce air-conditioning noise or temporarily shut off the air conditioning.
  • Use an 80 Hz highpass filter (low-cut filter).
  • Use microphones with limited low-frequency response.

NOISY (THUMPS)

  • Change the microphone position.
  • Change the musical instrument.
  • Use a highpass filter set around 40 to 80 Hz.
  • If the cause is mechanical vibration traveling up the mic stand, put the mic in a shock-mount stand adapter. Or use a microphone that is less susceptible to mechanical vibration, such as an omnidirectional mic, or a unidirectional mic with a good internal shock mount. *Use a microphone with a limited low-frequency response.
  • If the cause is piano-pedal thumps, work on the pedal mechanism. Maybe stuff a foam windscreen in there.

HUM
If you hear an unwanted tone at 50 Hz, 60 Hz, or their harmonics, that's hum. It might have an edgy sound like a buzz. Here are some brief tips on hum prevention:

  • Make sure equipment chassis are connected to ground through their power cords.
  • Plug all recording and musical equipment into outlet strips connected to the same power outlet. Don't plug into widely separated AC outlets.
  • Separate mic cables from power cables.
  • Be sure that mic-cable shields are soldered to their connectors on both ends of the cable.
  • With line-level cables, experiment with removing the shield connection at one end of the cable only.
  • On direct boxes and splitters, flip the ground-lift switch to the position where you monitor the least hum.
  • Use balanced lines and balanced equipment where possible, instead of unbalanced.
  • Don't use lighting dimmers or fluorescent lights, which can cause a buzz in the audio.
  • A cable going into a guitar amp might have become unplugged.
  • To reduce electric-guitar hum, have the player keep their hands in contact with the strings, and rotate to find a spot where the hum stops. Turn off compressor stomp boxes.

POP
Pops are explosive breath sounds in a vocalist's microphone. If your vocal recording has pops, try these solutions:

  • Stretch a silk stocking over a darning hoop, and mount it on a mic stand a few inches from the microphone (or use an equivalent commercial product).
  • Place a foam windscreen (pop filter) on the microphone.
  • Place the microphone above or to the side of the mouth.
  • Place the microphone farther from the vocalist.
  • Use a microphone with a built-in pop filter (ball grille).
  • Use an omnidirectional microphone, because it is likely to pop less than a directional (cardioid) microphone.
  • Switch in a highpass filter (low-cut filter) set around 80 Hz.

SIBILANCE
Sibilance is an overemphasis of "s" and "sh" sounds. If you hear sibilance in a vocal signal, try these steps:

  • Use a de-esser.
  • Place the microphone farther from the vocalist.
  • Place the microphone toward one side of the vocalist, rather than directly in front.
  • Cut equalization in the range from 5 to 10 kHz.
  • Change to a duller-sounding microphone.

BAD MIX
Maybe some instruments or voices are too loud or too quiet in your mix. Try this:

  • Change the mix (maybe change the mix engineer!)
  • Compress vocals or instruments that occasionally get buried.
  • Change the equalization on certain instruments to help them stand out.
  • If an instrument or vocal in a mix gets too loud or soft, ride gain on its fader. That is, move its fader to preset points at certain times in the mix to control the volume.

UNNATURAL DYNAMICS
When your pop-music recording has unnatural dynamics, loud sounds don't get loud enough or soft sounds disappear. If this happens, try these steps:

  • Check the tracking of noise-reduction units. For example, a 10 dB level increase at the input of the encode unit should appear as a 10 dB level increase at the output of the decode unit.
  • Use the same type of noise reduction during playback that was used during recording.
  • Use less compression or limiting.
  • Avoid overall compression.

ISOLATED SOUND
If some of the instruments on your recording sound too isolated, as if they are not in the same room as the others, follow these steps:

  • In general, allow a little crosstalk between the left and right channels. If tracks are totally isolated, it's hard to achieve the illusion that all the instruments are playing in the same room at the same time. You need some crosstalk or correlation between channels. Some right-channel information should leak into the left channel, and vice versa.
  • Place microphones farther from their sound sources to increase leakage.
  • Use omnidirectional mics to increase leakage.
  • Use stereo reverberation or echo.
  • Pan effects returns to the channel opposite the channel of the dry sound source.
  • Pan extreme left-and-right tracks slightly toward center.
  • Make the effects-send levels more similar for various tracks.
  • To give a lead-guitar solo a fat, spacious sound, use a stereo chorus. Or send its signal through a delay unit, pan the direct sound hard left and pan the delayed sound hard right.

LACK OF DEPTH
If the mix lacks depth, try these steps:

  • Achieve depth by miking instruments at different distances.
  • Use varied amounts of reverberation on each instrument. The higher the ratio of reverberant sound to direct sound, the more distant the track sounds.

PART 4: BAD SOUND IN A CLASSICAL MUSIC RECORDING
Check the following procedures if you have problems recording classical music:

TOO DEAD
If the sound of your classical recording is too dead -- there is not enough ambience or reverberation -- try these measures to solve the problem:

  • Place the microphones farther from the performers.
  • Use omnidirectional microphones.
  • Record in a concert hall with better acoustics (longer reverberation time).
  • Add artificial reverberation.

TOO CLOSE
If the sound is too detailed, too close, or too edgy, follow these steps:

  • Place the microphones farther from the performers.
  • Place the microphones lower or on the floor (as with a boundary microphone).
  • Roll off the high frequencies.
  • Use mellow-sounding micophones (many ribbon mics have this quality).

TOO DISTANT
If the sound is distant and there is too much reverberation, these steps might help:

  • Place the microphones closer to the performers.
  • Use directional microphones (such as cardioids).
  • Record in a concert hall that is less live (reverberant).

NARROW STEREO SPREAD
If your classical-music recording has a narrow stereo spread, try these steps:

  • Angle or space the main microphone pair farther apart.
  • If you're doing midside stereo recording, turn up the side output of the stereo microphone.
  • Place the main microphone pair closer to the ensemble.

EXCESSIVE STEREO SPREAD
If the sound has excessive stereo spread (or "hole-in-the-middle"), try the following:

  • Angle or space the main microphone pair closer together.
  • If you're doing midside stereo recording, turn down the side output of the stereo microphone.
  • In spaced-pair recording, add a microphone midway between the outer pair, and pan its signal to the center.
  • Place the microphones farther from the performers.

LACK OF DEPTH
Try the following to bring more depth into your classical-music recording:

  • Use only a single pair of microphones out front. Avoid multimiking.
  • If you must use spot mics, keep their level low in the mix.
  • If you are spot miking, add more artificial reverberation to the distant instruments than to the close instruments.

BAD BALANCE
Maybe some instruments are too loud or too soft. If your classical-music recording has bad balance, try the following:

  • Place the microphones higher or farther from the performers.
  • Ask the conductor or performers to change the instruments' written dynamics. Be tactful!
  • Add spot microphones close to instruments or sections needing reinforcement. Mix them in subtly with the main microphones' signals.

MUDDY BASS
If your recording has a muddy bass sound, follow these steps:

  • Aim the bass-drum head at the microphones.
  • Put the microphone stands and bass-drum stand on resiliant isolation mounts, or place the microphones in shock-mount stand adapters.
  • Roll off the low frequencies or use a highpass filter set around 40 to 80 Hz.
  • Record in a concert hall with less low-frequency reverberation.

RUMBLE
Sometimes your classical-music recording picks up rumble from air conditioning, trucks, and other sources. Try the following to clear this up:

  • Check the hall for background rumble problems.
  • Temporarily shut off the air conditioning.
  • Record at a time of day when there is less traffic.
  • Record in a quieter location.
  • Use a highpass filter set around 40 to 80 Hz.
  • Use microphones with limited low-frequency response.

DISTORTION
If your classical-music recording has distortion, try the following:

  • Switch in the pads built into the microphones (if any).
  • Increase the mixer input attenuation (turn down the input trim).
  • Check connectors for stray wires or bad solder joints.

BAD TONAL BALANCE
Bad tonal balance expresses itself in a sound that is too dull, too bright, thin, tubby or colored. If your recording has this problem, follow these steps:

  • Change the microphones. Generally, use flat-response microphones with minimal off-axis coloration.
  • Follow the 3:1 rule mentioned earlier.
  • If a microphone must be placed near a hard reflective surface, use a boundary microphone to prevent phase cancellations between direct and relected sounds.
  • Adjust equalization.
  • Place the mics at a reasonable distance from the ensemble (too-close miking sounds shrill).
  • Avoid mic positions that pick up standing waves or room modes. Experiment with small changes in mic position. The next time you hear something you don't like in a recording, the tips in this guide should help you define the problem and find a solution. Good luck!

Copyrighted 1999 by Deltamedia. May not be reproduced in whole or part without permission.